guides/user: use correct get nid command — radicle.xyz

the old command has been deprecated

 If you forget your DID or NID, you can query your full identity by running `rad
 self` or alternatively you can grab your DID with `rad self --did` and your NID
 with `rad self --nid`.
 with `rad node status --only nid`.
 ```
 $ rad self

     z6MkvZwzK64f3GuDcAs6dEcje89ddfHkBjS1v9Dkh7aCGq3C
 Does it look familiar to you? Well, it's your Node ID. Remember you can always
 check your Node ID by running `rad self --nid`.
 check your Node ID by running `rad node status --only nid`.
 When using Git with traditional forges, you are pushing to a remote which is a
 centralized server that all other collaborators are also using. In Radicle, the