Document Android setup and troubleshooting for bare RN app

Author: roncohen

packages/react-native-sdk/dev/bare-rn/README.md

@@ -24,6 +24,39 @@ sudo xcode-select -s /Applications/Xcode.app/Contents/Developer
 sudo xcodebuild -runFirstLaunch
 ```
 
+Prerequisites for Android:
+
+- Android SDK installed (via Android Studio recommended).
+- Android SDK packages required by this project:
+  - Android SDK Platform 36
+  - Android SDK Build-Tools 36.0.0
+  - Android SDK Platform-Tools (`adb`)
+  - Android Emulator
+- At least one emulator (AVD) created, or a physical Android device connected.
+
+Set Android environment variables (`~/.zshrc`):
+
+```sh
+export ANDROID_HOME="$HOME/Library/Android/sdk"
+export ANDROID_SDK_ROOT="$ANDROID_HOME"
+export PATH="$PATH:$ANDROID_HOME/platform-tools:$ANDROID_HOME/emulator:$ANDROID_HOME/cmdline-tools/latest/bin"
+source ~/.zshrc
+```
+
+Create `android/local.properties`:
+
+```sh
+printf "sdk.dir=%s/Library/Android/sdk\n" "$HOME" > packages/react-native-sdk/dev/bare-rn/android/local.properties
+```
+
+Sanity checks:
+
+```sh
+adb --version
+emulator -list-avds
+npx react-native doctor
+```
+
 From the repo root:
 
 ```sh
@@ -53,6 +86,22 @@ yarn ios
 yarn android
 ```
 
+If using a physical device:
+
+```sh
+adb devices
+adb reverse tcp:8081 tcp:8081
+```
+
+## Troubleshooting
+
+- `/.../adb: No such file or directory`
+  - `platform-tools` is missing or `ANDROID_HOME` / `PATH` is not set correctly.
+- `No emulators found as an output of emulator -list-avds`
+  - Create an emulator in Android Studio Device Manager, or connect a physical device.
+- `SDK location not found ... android/local.properties`
+  - Set `ANDROID_HOME` / `ANDROID_SDK_ROOT` and create `packages/react-native-sdk/dev/bare-rn/android/local.properties`.
+
 ## Notes
 
 - This app calls `@reflag/react-native-sdk` directly (no Expo runtime).