Add documentation and tag new release

Hi

Would you explain the recent changes in clerk.pl ? I can't figure :-\ 
I'm also curious about the 'musiclist' file and how to use it :)

Last but not least, could you tag a new release ? I plan to maintain a build script for Slackware (SlackBuild) and need an up-to-date tarball to download.

Thanks again for clerk, it's still my favorite !