AFAIK OTP releases are the recomended way of installing, but
* People seem unaware of that and use from source installations because they use the guide with the name of their distro
* People don't know what OTP releases are or what it means
I added a warning on all installation-from-source guides and added the same explanation on the two OTP pages (the miigration to OTP and installing OTP)
Since python doesn't have a way to lock deps for a particlar project
by default, I didn't bother with it. This resulted in mkdocs updating at
some point, bringing a breaking change to how tabs are declared and
broken tabs on docs-develop.pleroma.social. I've learned my lesson
and locked deps with pipenv in pleroma/docs!5. This MR updates Pleroma
docs to use the new tab style, fortunately my editor did most of it.
Closes #2045
