Please move the PR description into the commit message, since the project reviews individual commits.

Thank you! I added a description to the commit message

I don't think it's a common mistake to run jj bookmark track without setting up a remote. I'd typically run jj git clone or jj git remote add, then run jj git push -c/--named. There might be a better alternative depending on your workflow.

I generally like the idea of making the error messages as helpful as possible, but I think this might lead to some false positives.

1. The name origin is currently hardcoded in the hint message. If you try to track a bookmark with --remote=upstream and it can't find upstream, it will still tell you to run jj git remote add origin ....
2. The hint should probably explain what the command does instead of telling users to run it blindly. Something like "To add the missing remote, run ..." would be better.
3. (optional) It is not clear to me that a missing remote really is the most likely cause for the error. It might be more likely that the remote is just misspelled, in which case this hint is misleading. A check for a remote with a similar name would be a great enhancement to this PR.