`?` key for help

[abitrolly]

Now I need a keyboard shortcuts help. ) Like pressing '?' in GitHub to remind that are the abilities that godu provides beyond fat dir navigation.

[abitrolly]

It is quite easy to add a new key here

godu/parser.go

Line 30 in f0108a9

case tcell.KeyRune:

and not so easy to understand how draw and toggle help panel with content.

[abitrolly]

There is also a mistake in godu diagram https://github.com/viktomas/godu/blob/master/CONTRIBUTING.md#godu-architecture - no such class as InteractiveTree.

[viktomas]

There is also a mistake in godu diagram https://github.com/viktomas/godu/blob/master/CONTRIBUTING.md#godu-architecture - no such class as InteractiveTree.

Thanks @abitrolly for pointing this out. I've updated the diagram in #73 🎉