Clarify that the rad remote is the stored copy — radicle.xyz

Remote copy might be misleading for new users reading the guide. It’s probably worth emphasising that this a local operation.

        ecb1bf0..74fb8d2  master -> master
 Whenever you execute a `git push rad` command, you are pushing the changes in
 your local working copy to your remote copy. You see that the remote of your
 your local working copy to your `rad` remote, the stored copy managed by your
 radicle node, so it's a local operation. You see that the remote of your
 repository is represented by the URL:
     rad://z31hE1wco9132nedN3mm5qJjyotna/z6MkvZwzK64f3GuDcAs6dEcje89ddfHkBjS1v9Dkh7aCGq3C