adds manpage

Fixes #7.

It might make more sense not to include all the command help output (as I did here).

Instead, the page could just list the command summaries (as in the `wry help` output), only sorted into groups.

This would be accompanied by instructions to `wry help <command>` as needed for more info.

That isn't much better than the status quo, so I didn't do that. A good compromise might be to just pull in the summary + usage and leave the full gory details to `wry help <command>`. As a side benefit, it would be far more feasible to properly typeset the summary + usage lines.