Clarify proto3
diff --git a/README.md b/README.md
index 0d50f29..28d1aa3 100644
--- a/README.md
+++ b/README.md
@@ -5,14 +5,16 @@
This repository provides a plugin for the [protoc
compiler](https://developers.google.com/protocol-buffers/docs/cpptutorial#compiling-your-protocol-buffers).
-It generates Dart files for working with data in protocol buffers format. At
-this time we only support
-[proto2](https://developers.google.com/protocol-buffers/docs/proto), but proto3
-may work in simple cases due to backwards compatibility.
+It generates Dart files for working with data in protocol buffers format.
Requirements
------------
+We only support the full [proto2](https://developers.google.com/protocol-buffers/docs/proto)
+schema. Proto3 should work due to backwards compatibility. See
+[this issue list](https://github.com/dart-lang/protobuf/issues?q=is%3Aissue+is%3Aopen+label%3Aproto3)
+for proto3 schema features which are currently missing.
+
To compile a .proto file, you must use the 'protoc' command which is [installed
separately](https://developers.google.com/protocol-buffers/docs/downloads).
Protobuf 3.0.0 or above is required.
