Add Compatibility and Contributions to README (#33)

Adding these sections in response to:
https://stackoverflow.com/questions/58339015/kafka-connect-string-cannot-be-casted-to-struct
#28
#31

README.md

@@ -1,10 +1,17 @@
 # kafka-connect-protobuf-converter
-Converter plugin for [Kafka Connect](https://docs.confluent.io/3.2.0/connect/). A converter
+Converter plugin for [Kafka Connect](https://docs.confluent.io/current/connect/). A converter
 controls the format of the data that will be written to Kafka for source connectors or 
 read from Kafka for sink connectors.
 
+## Compatibility
+
+The 2.x release series is compatible with Kafka Connect 5.x. and up (older releases have been validated to work all the way back to Kafka Connect 3.2.0, although we highly recommend updating to the latest version).
+
+*N.B. This converter only works with `proto3` protocol buffer schemas.*
+
 ## Usage
-Copy the `kafka-connect-protobuf-converter` jar and the jar containing your protocol buffers to 
+
+Copy the `kafka-connect-protobuf-converter` jar and the jar containing your compiled protocol buffers to 
 `/usr/share/java/kafka-serde-tools` on your Kafka Connect instance and restart Kafka Connect.
 
 Converters can be specified on a per-connector basis.
@@ -143,7 +150,12 @@ message TestMessage {
 }
 ```
 
+## Contributing
+
+Contributions are warmly welcomed. If fixing a bug, please open an issue on the project before opening a PR. This helps with documentation for other users and will make code review go quicker 🙌
+
 ## Development
+
 #### Run tests:
 ```
 mvn test