hotkey tip on screen

[Deantwo]

As long as we get an option to turn off the help text in the options, I don't see an issue with adding it.

I would however maybe suggest it be added at the bottom in the somewhat middle of the screen. And of course not just simple black text, it would be impossible to read at night.

Maybe include the zoom and overview cycling keys. Not sure it is necessary to show the construction window or building window hotkeys.