[webview_flutter] Added contributing section to the README.md (#4543)

diff --git a/packages/webview_flutter/webview_flutter_android/CHANGELOG.md b/packages/webview_flutter/webview_flutter_android/CHANGELOG.md
index ae76ea8..71389de 100644
--- a/packages/webview_flutter/webview_flutter_android/CHANGELOG.md
+++ b/packages/webview_flutter/webview_flutter_android/CHANGELOG.md
@@ -1,5 +1,6 @@
-## NEXT
+## 2.3.1
 
+* Adds explanation on how to generate the pigeon communication layer and mockito mock objects.
 * Updates compileSdkVersion to 31.
 
 ## 2.3.0
diff --git a/packages/webview_flutter/webview_flutter_android/README.md b/packages/webview_flutter/webview_flutter_android/README.md
index 3883856..492ef91 100644
--- a/packages/webview_flutter/webview_flutter_android/README.md
+++ b/packages/webview_flutter/webview_flutter_android/README.md
@@ -7,6 +7,20 @@
 This package is [endorsed][2], which means you can simply use `webview_flutter`
 normally. This package will be automatically included in your app when you do.
 
+## Contributing
+
+This package uses [pigeon][3] to generate the communication layer between Flutter and the host platform (Android). The communication interface is defined in the `pigeons/android_webview.dart` file. After editing the communication interface regenerate the communication layer by running the `./generatePigeons.sh` shell script.
+
+Besides [pigeon][3] this package also uses [mockito][4] to generate mock objects for testing purposes. To generate the mock objects run the following command:
+```bash
+flutter packages pub run build_runner build --delete-conflicting-outputs
+```
+
+If you would like to contribute to the plugin, check out our [contribution guide][5].
+
 [1]: https://pub.dev/packages/webview_flutter
 [2]: https://flutter.dev/docs/development/packages-and-plugins/developing-packages#endorsed-federated-plugin
+[3]: https://pub.dev/packages/pigeon
+[4]: https://pub.dev/packages/mockito
+[5]: https://github.com/flutter/plugins/blob/master/CONTRIBUTING.md
 
diff --git a/packages/webview_flutter/webview_flutter_android/pubspec.yaml b/packages/webview_flutter/webview_flutter_android/pubspec.yaml
index 705951b..4bb1ebc 100644
--- a/packages/webview_flutter/webview_flutter_android/pubspec.yaml
+++ b/packages/webview_flutter/webview_flutter_android/pubspec.yaml
@@ -2,7 +2,7 @@
 description: A Flutter plugin that provides a WebView widget on Android.
 repository: https://github.com/flutter/plugins/tree/master/packages/webview_flutter/webview_flutter_android
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+webview%22
-version: 2.3.0
+version: 2.3.1
 
 environment:
   sdk: ">=2.14.0 <3.0.0"