Add ⌘ (mac command/looped square) symbol to Roboto Mono

[kevincannon]

Request:
Roboto Mono doesn't seem to have the mac command/looped square symbol. ⌘

It's a really great font to use to display keyboard shortcuts because it disambiguates nicely between letters like iIl1O0.

Unfortunately, not having the ⌘ symbol, means it falls back to a different font, which is a shame.