Add air quality

[Guthers]

Can be done using this API - https://aqicn.org/data-platform/token/#/

Ideally would have both a command and a daily update (forecast?) in #radar

Command could be something like !air if we decide we want multiple possible locations?

[Guthers]

Token is now an env var called AQI_API_TOKEN thanks @TRManderson