Update the trac update documentation

mu-plugins/blocks/global-header-footer/README.md

@@ -40,6 +40,22 @@ See `r18316-dotorg` for an example.
 
 Use the API endpoints to get the markup and styles. See `register_routes()` for the endpoints. Examples:
 
-* Trac: [`templates/update-headers.php`](https://github.com/dd32/wordpress.org/blob/c019f1ceb345310c472136d951f82d97fd517cda/trac.wordpress.org/templates/update-headers.php) in Meta SVN.
-* Codex: `grab-wporg-header-footer.sh` runs on a cron and updates `header.inc`, then `skins/codex/Codex.php` includes them. See `r14081-deploy`. Codex has heavy page caching, only systems can clear the page cache.
-* Planet: `planet/bin/generate-index-template.sh` in `dotorg`.
+**Trac**
+
+Make sure to update these files if any markup has changed!
+
+- Check out the folder locally (it wasn't on my sandbox)
+  ```
+  svn co https://meta.svn.wordpress.org/sites/trunk/trac.wordpress.org/templates
+  ```
+- Run `php templates/update-headers.php`. This script will use the header & footer rest API endpoints to parse out the markup, and sync it into the local trac template files ([source](https://github.com/wordpress/wordpress.org/blob/trunk/trac.wordpress.org/templates/update-headers.php)).
+- Check the changes & commit the updated templates.
+- No deploy needed, the templates are cached based on page hits, so they'll expire eventually.
+
+**Codex**
+
+`grab-wporg-header-footer.sh` runs on a cron and updates `header.inc`, then `skins/codex/Codex.php` includes them. See `r14081-deploy`. Codex has heavy page caching, only systems can clear the page cache.
+
+**Planet**
+
+`planet/bin/generate-index-template.sh` in `dotorg`.