Add one line description of each program to help text

Some of these programs I had no idea what they did (namei for example) and had to go and open the man page. Most other programs seem to show a 1 line description in the help text you get from `-h` or `--help`, so I've extracted these from the man pages and added to each program.

Also fixed a couple of tiny things in some man pages and the typo in zramctl that I put a bug report in for earlier