Update docs to include Dexguard keep resource rule

README.md

@@ -216,6 +216,10 @@ When Proguard is enabled (which it is by default for Android release builds), it
 
 `com.mypackage` should match the `package` value in your `app/src/main/AndroidManifest.xml` file.
 
+If using Dexguard, the shrinking phase will remove resources it thinks are unused. It is necessary to add an exception to preserve the build config package name.
+
+    -keepresources string/build_config_package
+
 ## Testing
 
 Since `react-native-config` contains native code, it cannot be run in a node.js environment (Jest, Mocha). [react-native-config-node](https://github.com/CureApp/react-native-config-node) provides a way to mock `react-native-config` for use in test runners - exactly as it is used in the actual app.