Add admin changelog PR text format to pull-request-guidelines (#282)

https://github.com/space-wizards/SS14.Changelog/blob/66c381d79c6ee14ba0a2530d4a50204f5d328818/SS14.Changelog/Controllers/WebhookController.cs#L31-L32

src/en/general-development/codebase-info/pull-request-guidelines.md

@@ -85,6 +85,34 @@ Each entry is either an `add`, `remove`, `tweak`, or `fix`. There can be multipl
 
 Maintainers may, at their discretion, add, modify, or remove a change log entry that you suggest.
 
+#### Admin changelog
+
+Putting `ADMIN:` in the changelog will place all changelogs below it into the admin changelog category instead of the main changelog category.
+
+Note: The category is case-insensitive, but if it is not alphabetical ending with a colon, it will fail parsing the category and will fall back to placing the changelogs in the previous category or the main changelog category.
+
+```
+:cl:
+ADMIN:
+- add: Added fun!
+- remove: Removed fun!
+- tweak: Changed fun!
+- fix: Fixed fun!
+```
+or
+```
+:cl:
+- add: Added fun!
+- remove: Removed fun!
+- tweak: Changed fun!
+- fix: Fixed fun!
+ADMIN:
+- add: Added fun!
+- remove: Removed fun!
+- tweak: Changed fun!
+- fix: Fixed fun!
+```
+
 ## Writing An Effective Changelog
 The Changelog is for *players* to be aware of new features and changes that could affect how they play the game. It is *not* designed for maintainers, admins, or server operators (these should be in the PR description).