Mention no proto 2, fixes #6

Author: danielgtaylor

README.md

@@ -2,7 +2,7 @@
 
 ![](https://github.com/danielgtaylor/python-betterproto/workflows/CI/badge.svg)
 
-This project aims to provide an improved experience when using Protobuf / gRPC in a modern Python environment by making use of modern language features and generating readable, understandable, idiomatic Python code. It will not support legacy features or environments. The following are supported:
+This project aims to provide an improved experience when using Protobuf / gRPC in a modern Python environment by making use of modern language features and generating readable, understandable, idiomatic Python code. It will not support legacy features or environments (e.g. Protobuf 2). The following are supported:
 
 - Protobuf 3 & gRPC code generation
   - Both binary & JSON serialization is built-in