Add local development instructions to README

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: markrcote

README.md

@@ -14,14 +14,52 @@ An Android app for tracking [German Volume Training](https://www.t-nation.com/tr
 
 - Android 7.0 (API 24) or higher
 
-## Building
+## Local Development
 
-Open the project in Android Studio and build normally, or from the command line:
+### Prerequisites
 
+- [Android Studio](https://developer.android.com/studio) (recommended), or Android SDK with command-line tools
+- JDK 17 or higher
+
+### Setup
+
+1. Clone the repository:
+   ```bash
+   git clone https://github.com/markrcote/gvtimer.git
+   cd gvtimer
+   ```
+
+2. Open in Android Studio (**File > Open**), or use the command line directly.
+
+### Building
+
+```bash
+./gradlew assembleDebug     # debug build
+./gradlew assembleRelease   # release build
+```
+
+### Running on a device or emulator
+
+**Android Studio:** Select a device (or create an emulator via **Device Manager**) and click **Run**.
+
+**Command line — start an emulator:**
+```bash
+# List available AVDs
+emulator -list-avds
+
+# Start one (replace <avd-name> with an AVD from the list above)
+emulator -avd <avd-name> &
+```
+
+**Command line — install and run:**
 ```bash
-./gradlew assembleRelease
+./gradlew installDebug      # installs debug build on connected device/emulator
 ```
 
+### Making UI changes
+
+All timer logic and UI lives in a single file: `app/src/main/assets/index.html`. You can edit this file directly in any text editor — no Android-specific tooling required. After editing, rebuild and reinstall to see changes.
+
 ## Architecture
 
 The app is a thin Android wrapper (Kotlin + Jetpack Compose) around a self-contained HTML/CSS/JavaScript web app loaded from the local assets. The web app handles all timer logic and UI.