Write security-announce.txt

Title: Keeping Track of Updates
Section: Security and Maintenance
File name: security-announce.txt
Covers: Get announcements about security releases, know when you need to update, the module updates page
Index: Security

Attribution

See https://userguide_new-drupal.dev.devdrupal.org/guidelines/guidelines.htm...
[Fill in!]

Checklist for this phase

- Does it follow the template?
- Have the comments and placeholder text been removed from the template?
- Is everything the topic was supposed to cover included, and nothing extra?
- If there are @todo notes, are they clear?
- If there are images included, do they include instructions for how to redo them in a comment? (Note: Screenshots do not need to be perfect. Just make a rough cut.)
- Is attribution provided?