add a bit more to README.md

README.md

diff --git a/README.md b/README.md
index 3f4ed79..3b3451d 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,8 @@
 # Bazel Persistent Worker API
 
 This repository contains the code for Bazel's [Persistent Worker](https://bazel.build/remote/persistent) API.
+
+There are two Bazel modules in this repository:
+
+* [**proto**](https://github.com/bazelbuild/bazel-worker-api/tree/main/proto): contains the bare protocol buffers for the worker API.
+* [**java**](https://github.com/bazelbuild/bazel-worker-api/tree/main/java): contains a simple Java wrapper library.