This is a followup commit to #30824.
Fixes
https://chat.zulip.org/#narrow/stream/9-issues/topic/.F0.9F.8E.AF.20help.20not.20updated.20for.20new.20preferences.20sections/near/1899330.
git grep in the help directory will still show up results for `Advanced`
but those are mostly used in either plain english language instructions
or refer to some other part of the app. At the point of writing this
commit, there were 6 results for `Advanced`, 4 of which were plain
english, 1 refers to the Advanced settings in chrome for desktop
notifications, and another one refers to `Advanced configurations` for
channel settings.
- Corrects documentation to reflect that typing notifications also
work when narrowing to all direct messages in the web/desktop app,
and disappear under certain conditions.
These files are not Jinja2 templates, so there's no reason that they needed
to be inside `templates/zerver`. Moving them to the top level reflects their
importance and also makes it feel nicer to work on editing the help center content,
without it being unnecessary buried deep in the codebase.
