This is documented on the page about organization language, but makes sense
to include here as well.
Also reordered preferences to match the order in the menu.
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.