Update README.md with gradle instructions for java

java/README.md

@@ -13,7 +13,11 @@ generate Java code for your .proto files:
     $ protoc --java_out=${OUTPUT_DIR} path/to/your/proto/file
 
 Include the generated Java files in your project and add a dependency on the
-protobuf Java runtime. If you are using Maven, use the following:
+protobuf Java runtime.
+
+### Maven
+
+If you are using Maven, use the following:
 
 ```xml
 <dependency>
@@ -37,6 +41,14 @@ protobuf-java-util package:
 </dependency>
 ```
 
+### Gradle
+
+If you are using Gradle, add the following to your `build.gradle` file's dependencies:
+```
+    compile 'com.google.protobuf:protobuf-java:3.6.1'
+```
+Again, be sure to check that the version number maches (or is newer than) the version number of protoc that you are using.
+
 ### Use Java Protocol Buffers on Android
 
 For Android users, it's recommended to use protobuf Java Lite runtime because