Fix running from PATH and add better usage/manpage (#5) * Misc changes - Don't segfault when ran from PATH - Remove useless `-u` arg from usage - Elaborate on usage * Add manpage * usage: Use spaces not tabs * Add snaputil -o This will query the IORegistry to determine what the system apfs snapshot's name should be. * Update manpage Co-authored-by: Cameron Katri <me@cameronkatri.com>