README: the Tangled mirror and the Radicle repository ID
The repository now has three homes carrying the same history, and a Radicle
repository is findable only by its ID, so a README that leaves it out has left
out the one thing a reader needs in order to seed or clone it.
The clone command stays the https form. Documentation is read by people with
no account on the server and no key registered with it, and for them the ssh
URL fails with a permission error before it reaches the repository; the remote
itself stays ssh, because that is what pushes. `git ls-remote` over https
answers with no credentials, so the URL written here is one that works.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016LJuBzNgYqy1qhVusk5VZY