When you would run `install.sh -h` or with `--help` flag, it would print those two `echo` lines, but it'd continue on its merry way, installing everything still! A `help` flag is not supposed to do that! So I added an `exit 0` to the help flag.
This fixes the scopatz/nanorc#130 issue by preventing the install script
to sort the ~/.nanorc config file, and only add includes if they're not
already present.