chore: fix gapic-generator-java/DEVELOPMENT.md link in README.md (#3275)

Fixes #3274

README.md

@@ -7,7 +7,7 @@ For more information, please refer to [rename a repository](https://docs.github.
 This repository consists of the following modules:
 
 - **[gapic-generator-java](./gapic-generator-java/README.md)**: the Protobuf compiler plugin to generate Java code.
-  See [gapic-generator-java/DEVELOPMENT.md](./gapic-generator-java/README.md) for setup.
+  See [gapic-generator-java/DEVELOPMENT.md](./gapic-generator-java/DEVELOPMENT.md) for setup.
 - **[gax-java](./gax-java/README.md)**: the runtime library required for Google Cloud client libraries,
   including the ones generated by gapic-generator-java.
 - **[java-common-protos](./java-common-protos/README.md)** and **[api-common-java](./api-common-java/README.md)**: Protobuf-generated common