Add instructions for rad-cli

[ghost]

The docs are mostly written for upstream which some radicle-cli commands in there. For example, submitting a patch is only with upstream commands, while creating a project is only with rad commands.

It would be great if there were a version of the instructions for radicle-cli and another for upstream.

Maybe something like this

[joelhans]

Thanks for the feedback. I'll be working on removing all the Upstream content this week, which should clarify some of this. But I'll also likely end up moving much of the content about performing specific tasks into more use case-driven guides—something like, How to collaborate with your peers on a Radicle project. Stay tuned!

[joelhans]

Currently blocked by radicle-dev/radicle-cli#259

[joelhans]

Closing, as this work will likely fall to the Clients team.