Add an example on how to *add* a %wheel line to sudo - tricky as it has
a colon, which needs some special attention.
Add Linux-style path for sudoers file, to be consistent with other examples.
Merge pull request #2078 from huberteff/e2158b661d250c04609e7faff4d8e67df9cb37e4

Add example for adding to sudoers file