Limitations of `--empty` flag

### Contributions

- [x] I have read the contribution docs, and understand what's expected of me.

### Link to the page on docs.getdbt.com requiring updates

https://docs.getdbt.com/docs/build/empty-flag

### What part(s) of the page would you like to see updated?

There are some caveats / limitations to the `--empty` flag, and it would be helpful to call those out.

See https://github.com/dbt-labs/dbt-utils/issues/1009 for more detail.

### Additional information

_No response_