Update Readme - Questions

[raakasf]

It is not clear from the documentation what all datasources are supported. Does it only work with Prometheus? Could someone write a guide as to how to add other datasources or even custom datasources?

Thanks.

[K-Phoen]

For now, Prometheus and Stackdriver are supported.

Examples of implementation can be found here: https://github.com/K-Phoen/grabana/tree/fe555f94bfabc7c933fd502da47e25d4e65cac04/target