Improve docs around controller support and SDL mapping

While the [current docs](https://github.com/HarbourMasters/Shipwright/blob/develop/docs/GAME_CONTROLLER_DB.md) on game controllers is sufficient for someone who understands SDL and how to update `gamecontrollerdb.txt`, I assume most casual users will still not understand why their controller is not showing up or not working, nor how to fix it.

I think an overview of how to update `gamecontrollerdb.txt` with the latest from the community repo, and how to create and add new mappings with [SDL2 Gamepad Tool](https://www.generalarcade.com/gamepadtool/) would go a long way to help users.

I am happy to create a pull request for a first draft if you think this is useful. I created a [blog post](https://blog.yo1.dog/fix-ship-of-harkinian-does-not-recognize-controller-but-windows-does/) when I could not find these answers initially myself.

Out of scope: Would be cool if there was a warning or something within SoH settings menu when a controller was connected but no mapping was found. Could even point the user to the controller docs.