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.