Add usage section / cheatsheet

[maxelkins]

@grega How do you feel about changing this section to be more along the lines of whats in the usage section in the readme?

My thoughts were currently this feels too similar to the demo gif

Current:

Something along these lines but a little more "designed"

[grega]

Agreed on being too similar to the demo gif. I think finding a sweet spot between "enough to get you going" and "too much and overwhelming" is perhaps needed?

ie. leave the full usage docs on GitHub for all subcommands / flags / options, and cover the most useful subset here (for example, focus more on the interactive elements, and less on probably niche utilities like JSON output).

What do you think?