Use the README.txt template for the admin_toolbar_tools submodule

Problem/Motivation

The README.txt file don't use the proposed template https://www.drupal.org/docs/develop/documenting-your-project/readme-temp...

Proposed resolution

Edit the README.txt file according to the https://www.drupal.org/docs/develop/documenting-your-project/readme-temp...

Remaining tasks

None.

User interface changes

None.

API changes

None.

Data model changes

None.