Public read-only git client support

Like if it was placed on keybase://public/hattshire/pubgittst (I can clone it actually, but don't know if anyone can clone it too)

Keybase's CLI and GUI only gives the option to create private or team repos, but I can generate a public one by cloning an nonexistent one (Don't know if it publically works though).

The issue mentions Keybase's CLI and GUI and public repositories at a keybase:// URL, but no files or tests are identified. Start by determining how repository creation and cloning are currently exposed, then verify the expected behavior for a non-owner cloning a public repository; done means the supported client interfaces clearly provide working read-only public access.

Written by the indexing model from the issue text.