The wiki-editing paragraph described a push to <repo>.wiki.git, which no
longer exists (#170). A wiki lives at .gitbay/wiki/ on the default branch, so
editing one is editing a file.
Also records what that does not buy: the web editor reaches a wiki only on repositories that permit server-authored commits. One requiring verified signatures refuses, because the server signs nothing on a user's behalf, so those wikis stay push-only — this repository among them.
Ref #170.