a simple help file would suffice, no need for anything ingame. maybe a wiki page? anyway, the problem is that programmers usually don't like writing documentation. if someone would volunteer to write a manual and keep it up to date i'm sure simon wouldn't mind including it.
Better yet, why not a help button which opens up the wiki, either in pt itself, or in a browser. It would be even better if a search box in tp allowed the user to open the wiki with search results.