Add Meshtastic reader Flutter app (#483)

* Add Meshtastic reader Flutter app

* fix review comments

app/README.md

@@ -0,0 +1,15 @@
+# Meshtastic Reader
+
+Meshtastic Reader – read-only PotatoMesh chat client for Android and iOS.
+
+## Setup
+
+```bash
+cd app
+flutter create .
+# then replace pubspec.yaml and lib/main.dart with the versions in this repo
+flutter pub get
+flutter run
+```
+
+The app fetches from `https://potatomesh.net/api/messages?limit=100&encrypted=false`.