Add FAQ.md with information for common use cases. FAQ.md is supposed to provide extra documentation for Rover, based on common queries from users. It's a good place to put detailed information that doesn't fit the manual. The file rover.sh has been removed and an explanation for it has been added in FAQ.md instead. The same should be done for any helper script that might become worth of mention in the future. That way we don't clutter the repository with files that aren't part of a Rover basic setup.