It's not clear what DBs are supported by the Versatile Data Kit

**What is the feature request? What problem does it solve?**
Can you provide a list of the supported DBs for the Versatile Data Kit project. It would be very helpful for the new users of the project.

**Suggested solution**
Put together a wiki page which describes the supported DBs. It would be great to list the various capabilities of the DBs, e.g. query level support, templates, etc. 