Note in docs that live deploys don't set action output

### The use case you're trying to solve

The docs detail the action outputs, but those outputs are only set for preview deploys, not for live deploys (which have an early return before the outputs are set).

### Change to the action that would solve that use case

Add outputs to the live deployments, or add a note to the docs saying that live deploys don't have outputs.

### Other considerations

With the preview deployments, I use the action outputs to get the deployment URL, and use that to create a Github `deployment_status` event with the appropriate URL (and trigger various automated check workflows off that event). It took me a while to figure out why that wasn't working for live deployments. I worked around it by hardcoding the production URL into the event creation for production releases, which is reasonable, but I still think either the code or docs should be updated.