Add help screen

[SohamKukreti]

I have added a help screen to the game which explains the rules of the games and how to play it. The help screen can be opened by pressing 'h' key and can be closed by pressing 'esc' key.

If required, I can create a button instead of mapping keys to open the help screen.

[quozl]

Branch has conflicts after previous pull requests merged. Please rebase. You can avoid that in future by providing a merged branch in advance.

A screenshot in the pull request would have been useful.

Reviewed. The help has superfluous words in vague meanings;

• "the game consists" - wrong, the game is in the motions, not the playing board,
• "simply click" - wrong, there's no need for the click to be simple, some people may struggle,

There are too many constants.

I suggest placing the help in a list and iterating over it.

[SohamKukreti]

Thank you for the review. I'll work on the aforementioned points.