Add product compatibility matrix to docs

Please add a product compatibility matrix to README.md that covers the following information for each release of the Kafka Connector:

1. Connector version (e.g. 1.2)
2. Couchbase Server Version(s) (e.g. 4.x)
3. Kafka release versions (e.g. 0.8, 0.9)

See the Elasticsearch plugin for a model:
https://github.com/couchbaselabs/elasticsearch-transport-couchbase

The compatibility matrix should cover connector versions 1.0, 1.1, and 1.2