Fix and document process to update the web wikis

The web wikis are supposedly synchronised, but since a while they are out of sync.

AFAIK, the main wiki is at https://gitlab.torproject.org/tpo/web/wiki/ and it should appear under wiki in https://gitlab.torproject.org/tpo/web/community/-/wikis/home , https://gitlab.torproject.org/tpo/web/support/wikis/home, https://gitlab.torproject.org/tpo/web/manual/-/wikis/home etc.

But there is a big 'edit' button on each of the wikis, and changes have been made to the different versions

We should:

• Unify the updates on the main wiki
• Remove the edit buttons or make sure they go to the proper wiki to edit
• Document the best way to edit and check that it works.