Add help popup with keyboard shortcuts etc

[kimusan]

The app is nice but lacks a bit of user-friendliness. There really isn't any documentation (that I can find) for how to e.g. exit the app and do other things.
I hope that ctrl-C isnt the proper way of exiting the app :-)

please add something like a help menu item or ctrl-h for help popup.,

[dagleykd]

Seconding this - I really like the app, but having an option to click on that display keyboard shortcuts would be great as there are many and they can get confusing to try and do by memory.