mangohud: update page

[Managor]

• The page(s) are in the correct platform directories: common, linux, osx, windows, sunos, android, etc.
• The page(s) have at most 8 examples.
• The page description(s) have links to documentation or a homepage.
• The page(s) follow the content guidelines.
• The page(s) follow the style guide.
• The PR title conforms to the recommended templates.
• Version of the command being documented (if known):

[gutjuri]

I'd prefer RightShift

[spageektti]

I'd prefer RightShift

Then what about changing ArrowRight to RightArrow?

[Managor]

I prefer to keep arrow keys the way it is. With <ArrowRight> the mental flow is "arrow keys" and then "the direction" and it's uniform with <ArrowKeys>. It's also visually distinct from <RightClick>