Reference env vars in help message

[lmamakos]

It would be really useful if the help text for the --token and --server options referenced the available environment variables (HASS_TOKEN and HASS_SERVER) that can also be set up by the user. You have to dig around a bit to discover what these are, otherwise. This seems like one obvious place to note them; perhaps there are other places in the --help output that would be more consistent with existing style.

Thanks for the really wonderful tool!

[fabaff]

It's covered in the README. But if it's helps could be added to --help.

[lmamakos]

Thanks, that's great! The README is great, but not obviously available if someone does pip install homeassistant-cli