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
Large part of it was no longer true (i.e none of the changes need
recompilation anymore and you can't brick an instance by changing them,
it's not necessary to manually truncate the db manually anymore)
