document behaviour if applied to class methods

[gdamjan]

It's not clear what to do if you want to decorate class methods.

[minimind]

I've added the new decorator add_method and added it's use to the README here. Tell me if it's what you need.

[gdamjan]

hmm. what is self when the dispatched method is called?

[minimind]

Good point. I will take a look.

[gdamjan]

maybe first export two functions that do register and match, and then we'll see how to use in classes