Migrate documentation to new documentation system

Problem/Motivation

Recently, Drupal.org got a new documentation system for contrib modules. The Payment module's documentation still uses the old system, because when I try to view the current Payment documentation, I see the warning message:

This documentation needs to be migrated into the new documentation system. If you are a project maintainer, create a new documentation guide for your project first and then migrate this documentation.

I would like to add new pages to the Payment documentation about the Drupal 8 version, which has some different features / paradigms than the Drupal 7 version (to which the current documentation pertains), but I'd like to do that in the new documentation system if possible, to avoid creating extra work for this module's maintainers in the future.

Proposed resolution

The Payment maintainers (or someone with sufficient privileges) will need to:

1. Go to https://www.drupal.org/project/payment
2. Click "Edit" at the top
3. Scroll all the way down to the vertical tabs section, and find the "Project documentation" vertical tab.
4. At the bottom, in the text "Create a new Drupal 7 or Drupal 8 guide", click "Drupal 7". Fill out the "Create Documentation guide" form, and click "Save".
   Suggested data:
   • Title: Payment
   • Language: English
   • Summary: Payment 7.x is a generic payment platform which allows other modules to use any of the payment methods that plug into Payment.
   • Description: Payment 7.x is a generic payment platform which allows other modules to use any of the payment methods that plug into Payment. With Payment we only need one <strong>one</strong> <a href="/project/paypal_payment">Paypal</a>, <strong>one</strong> credit card and <strong>one</strong> <a href="/project/ideal">iDEAL</a> module to use with every single webshop or payment form that you want (applies to any payment method that works with Payment). This shortens development time and improves support, because only one instead of three Paypal modules need to be maintained, and simplifies UX, because all payment (method) information is now located in one place.<br />Module Page: https://www.drupal.org/project/payment
   • Status: - None -
   • Leave all the other fields at their default values.
   • Click "Save"
   • Take note of the NID for this new documentation guide: you'll need it for setting a number of node reference fields below.
5. Go to https://www.drupal.org/project/payment
6. Click "Edit" at the top
7. Scroll all the way down to the vertical tabs section, and find the "Project documentation" vertical tab.
8. At the bottom, in the text "Create a new Drupal 7 or Drupal 8 guide", click "Drupal 8". Fill out the "Create Documentation guide" form, and click "Save".
   Suggested data:
   • Title: Payment
   • Language: English
   • Summary: Payment 8.x is a generic payment platform which allows other modules to use any of the payment methods that plug into Payment.
   • Description: Payment 8.x is a generic payment platform which allows other modules to use any of the payment methods that plug into Payment. With Payment we only need one <strong>one</strong> <a href="/project/paypal_payment">Paypal</a>, <strong>one</strong> credit card and <strong>one</strong> <a href="/project/ideal">iDEAL</a> module to use with every single webshop or payment form that you want (applies to any payment method that works with Payment). This shortens development time and improves support, because only one instead of three Paypal modules need to be maintained, and simplifies UX, because all payment (method) information is now located in one place.<br />Module Page: https://www.drupal.org/project/payment
   • Related content: (link to the Drupal 7 documentation guide)
   • Status: - None -
   • Leave all the other fields at their default values.
   • Click "Save"
   • Take note of the NID for this new documentation guide: you'll need it for setting a number of node reference fields below.
9. Edit the Drupal 7 documentation guide again, and set the Related content field to refer to the Drupal 8 documentation guide page.
10. Go to the existing Payment documentation page at https://www.drupal.org/node/1704126
11. In the "This documentation needs to be migrated" warning, click "migrate this documentation", which should take you to https://www.drupal.org/migrate/documentation/1704126
12. Select the Drupal 7 documentation guide you created earlier from the select box, click "Continue", and proceed with the migration process. Click "Confirm" to begin the migration.
13. Go to https://www.drupal.org/project/payment
14. Click "Edit" at the top
15. In the "Summary" field, find the "For more information" unordered list, and modify the "Payment handbook" item to link to both new documentation pages.
16. In the "Description" field, find the "Installation and Usage" section, and modify the text on the project page to link to both new documentation pages.
    1. Find the "For more information" unordered list, and modify the "Payment handbook" item to link to both new documentation pages
    2. Find the "Payment methods" section, and check that the "see the handbook" still works; if not, link to the corresponding D7 documentation page
17. Scroll all the way down to the vertical tabs section.
18. In the "Resources" vertical tab, empty the "Documentation" field.
19. In the "Project documentation" vertical tab, check that the link to the Drupal 7 and 8 documentation guides you just made are set (if you followed the steps above to create the documentation guides, they should be set already).
20. Click "Save" to finish editing the project page.

Note: I have sufficient privileges on Drupal.org to do all of this for you if you'd like.

Remaining tasks

1. Create D7 documentation guide (steps 1–4 above).
2. Create D8 documentation guide (steps 5–8 above).
3. Set D8 documentation guide to be related to D7 documentation guide (step 8 above).
4. Set D7 documentation guide to be related to D8 documentation guide (step 9 above).
5. Migrate the old documentation into the D7 documentation guide (steps 10–12 above).
6. Modify the Payment project page summary to link to the new documentation guide (step 15 above).
7. Modify the Payment project page description to link to the new documentation guide (step 16 above).
8. Modify the Payment project page resources to remove link to the old documentation (step 18 above).
9. Check that the Payment project documentation links go to the new guides (step 19 above).
10. Update README.md and PLUGINS.md in the 8.x-2.x branch to link to the new documentation — note that I can't write a patch until the documentation has been migrated and we know the path of the new D8 handbook.
11. Update README.txt in the 7.x-1.x branch to link to the new documentation (note that DEVELOPERS.txt does not link to the documentation) — note that I can't write a patch until the documentation has been migrated and we know the path of the new D7 handbook.
12. Mark this issue as fixed.

User interface changes

N/A.

API changes

N/A.

Data model changes

N/A.