Added Usage help message to indicate '-a' invokes all checks. Removed 'sudo' exists check, replaced with appropriate 'su' check.
Fix a bug of finding user readable file in /etc/sudoers.d ``` for filename in /etc/sudoers.d/*; do echo $filename # filename is a array done ``` ``` for filename in '/etc/sudoers.d/*'; do echo $filename # filename is a single long string done ```
