Update docs/world maintainer.md

Co-authored-by: Exempt-Medic <60412657+Exempt-Medic@users.noreply.github.com>

docs/world maintainer.md

@@ -26,8 +26,17 @@ Unless these are shared between multiple people, we expect the following from ea
 ### Adding a World
 
 When we merge your world into the core Archipelago repository, you automatically become world maintainer unless you
-nominate someone else (i.e. there are multiple devs). You can define who is allowed to approve changes to your world
-in the [CODEOWNERS](/docs/CODEOWNERS) document.
+nominate someone else (i.e. there are multiple devs).
+
+### Being added as a maintainer to an existing implementation
+
+At any point, a world maintainer can approve the addition of another maintainer to their world.  
+In order to do this, either an existing maintainer or the new maintainer must open a PR updating the
+[CODEOWNERS](/docs/CODEOWNERS) file.  
+This change must be approved by all existing maintainers of the affected world, the new maintainer candidate, and
+one core maintainer.  
+To help the core team review the change, information about the new maintainer and their contributions should be
+included in the PR description.
 
 ### Getting Voted