How do I add a twitter icon like on Grav's menu?

I want to add a Twitter Icon to my navigation menu, how do I do this?

With Antimatter it’s easy:

That is a feature provided by themes, so if you extend that you’re good to go. Otherwise that needs to be added to the theme.
Antimatter is Grav’s “go-to” theme, the one you should most probably start with.

Thanks I got it working.