Improve error when importing certain modules in the `cmdline` package

Recently got
```
Critical: potential `verdi` speed problem: `aiida.orm.fields` module is imported which is not in: ('aiida.brokers', 'aiida.cmdline', 'aiida.common', 'aiida.manage', 'aiida.plugins', 'aiida.restapi')
```
Took a second to understand that it was due to me importing the orm package in the `cmdline` package. The above error could perhaps be a bit clearer. Will open a PR to improve. 