Add documentation about setting up keystore (#920)

README.md

@@ -66,7 +66,7 @@ You can alternatively install the build from PlayStore or F-Droid.
 3. Pull in all submodules with `git submodule update --init --recursive`
 4. Enable repo git hooks `git config core.hooksPath hooks`
 5. Setup TensorFlowLite by executing `setup.sh`
-6. For Android, run `flutter build apk --release --flavor independent`
+6. For Android, [setup your keystore](https://docs.flutter.dev/deployment/android#create-an-upload-keystore) and run `flutter build apk --release --flavor independent`
 7. For iOS, run `flutter build ios`
 
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