Readme updates (#476)

* Update README.md

- Add developer docs

* Remove RELEASE.md

README.md

@@ -12,3 +12,44 @@ Written in the [Flutter](https://flutter.dev/) environment, the app provides nat
 ## User Documentation
 
 User documentation for the InvenTree mobile app can be found [within the InvenTree documentation](https://inventree.readthedocs.io/en/latest/app/app/).
+
+## Developer Documentation
+
+For developers looking to contribute to the project, we use Flutter for app development. The project has been tested in Android Studio (on both Windows and Mac) and also VSCode.
+
+### Invoke Tasks
+
+We use the [invoke](https://www.pyinvoke.org) to run some core tasks - you will need python and invoke installed on your local system.
+
+### Getting Started
+
+Initial project setup (after you have installed all required dev tools) is as follows:
+
+Install required flutter packages:
+```
+flutter pub get
+```
+
+Generate initial translation files:
+
+```
+invoke translate
+```
+
+You should now be ready to debug on a connected or emulated device!
+
+### Building Release Versions
+
+Building release versions for target platforms (either android or iOS) is simplified using invoke:
+
+Build Android release:
+
+```
+invoke android
+```
+
+Build iOS release:
+
+```
+invoke ios
+```