Communities should be aware that MediaWiki:NewcomerTasks.json file can have effect on their newcomers, and should be informed on how to edit it. This relates to Growth-Scaling a bit, but it's an improvement rather than a blocker, so not tagging that tag.
This is filled as a follow-up to this comment by @Tgr:
We should add a message editnotice-8-NewcomerTasks.json to inform communities about how they can maintain the file, linking to docs.
@Tgr: Where are the docs, please? I can't find anything at mediawiki.org.