Document keyboard shortcuts

[iandunn]

Pressing s on a page like https://developer.wordpress.org/reference/hooks/edit_custom_thumbnail_sizes/ will open the search menu. I never knew that, though. Adding a ? shortcut is common for documenting them. Examples from GitHub and Stack Exchange:

That still doesn't solve the problem of folks knowing to press ? in the first place, though. For that, I can think of a few options:

• Add (accessible) tooltips that contain the shortcut:
  
• Show a keyboard icon in the header, clicking on it opens the modal
  
• Show the modal the first time someone visits the site, like how wp-admin has the "admin pointers"

Eventually, we could consider expanding this to all of w.org, with the list of shortcuts being determined by the current site, but the interface always remaining the same.

Related:

• https://core.trac.wordpress.org/ticket/33566
• Use ? and Alt+? to open keyboard shortcuts panel gutenberg#10914