Need documentation for air quality modeling (Online-CMAQ)

[chan-hoo]

Description

Since the online-cmaq branch was merged into the authoritative develop branch, the description for the air quality modeling (Online-CMAQ) should be added to the document of the UFS SRW App.

Solution

There would be two steps for documentation:

1. Add the quick start guide on the wiki (https://github.com/ufs-community/ufs-srweather-app/wiki/Air-Quality-Modeling) to the document shortly.
2. Add the details to the document in the near future.