Formulate a FAQ/troubleshooting page in the docs

There are quite a few common pitfalls that come up over and over again. We should really just have a troubleshooting page. Some ideas of what should go there:

• Docs are generally not deploying?
  • Are things showing up on the gh-pages branch?
  • Is DOCUMENTER_KEY properly set up?
  • Is CI for docs starting at all?
  • Is deploydocs running? If not, what error do you see? If yes, does it show git push to somewhere?
• master shows up, but not tags?
  • Is TagBot working? Is it using DOCUMENTER_KEY?
  • Can you see the tags in your GHA logs?

Would be good to collect other common errors and issues people run into as well.