The whole thing should ideally have a quick modal with hotkeys when you first open it (and a small button to bring it up again if needed).

Modals are the worst ux in games.

If it's only a few buttons anyway you can just show them somewhere as hints while the user isn't giving input or until they used then.

Eg just show a "m for Map\nspace to fire" until the user used each, hiding them each when the m/space is used respectively for that session (session storage so it shows up again if the user comes back later)