Document usage of keyboard input shortcuts

Description

The keyboard input element is used to inform the user of which keyboard key they need to press in order to perform an action via keyboard.

Questions that the documentation should answer

• When do we write opt vs ⌥? Or do you write both?
  • Use full words "option" and "command" #1129 (comment 1199034560)
• How do we handle differences between Windows and Mac keyboard shortcuts?

Relates to #1123 (closed)

Checklist

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