Controller support helpers

- Suggestions for approaches to use and to avoid
- Mention elements that don't work well with controller (ex. tooltips on arbitrary things you can't focus)
- How to test controller support without a controller (maybe <https://www.rewasd.com/releases/release-5.2.0>?)

Don't panic:
> There is focus recovery logic still in game, so this should not happen even if the UI is misconfigured
-Arch