Proposal: Readme update

[ErikEJ]

Maybe update the readme to indicate that Microsoft.Build.Sql and MsBuild.Sdk.SqlProj projects are also supported, and do not require a Windows build agent?

[JerrettDavis]

Added throughout with #14. Please let me know if you have any additional notes.

[ErikEJ]

Great, will have a look once it's merged

[ErikEJ]

Something went slightly wrong:

[ErikEJ]

Still see plenty of .sqlproj references:

[JerrettDavis]

Took another pass at it in #18.