Add a `HelpMenu` submenu component to explain the basics of the game

[jaohara]

Add a `HelpMenu` submenu component to explain the basics of the game

[jaohara]

This could be reached from TitleMenu and give a very short overview of the game basics + advanced strategy such as figuring out which squares need to be filled in common scenarios.

These include:

• A number that is more than half of the row/col, meaning number - (size / 2) squares on each side of the midpoint are filled
• A number in a column near a the edge of a filled row or vice versa, indicating that you can use that filled row as an anchor
• A set of multiple small numbers that can only fit one (or a few) ways due to the spacing between each one (2 2 2 1 on a 10x10, for example)
• Any other ones you can think up