Update README.md - Add info about plist removal

[avoidik]

The plist file must be deleted too, otherwise a LaunchDaemon will be loaded again after reboot.

[AkihiroSuda]

Thanks, but please sign the commit for DCO
https://github.com/apps/dco

(run git commit -a -s --amend, and make sure that the Signed-off-by: NAME <EMAIL> line with your real name is included in the commit message)