Add start.sh script for easy startup with virtual environment

Features:
- Automatically activates .venv virtual environment
- Creates venv if it doesn't exist
- Installs dependencies on first run
- Checks for configuration file
- Changes to project directory automatically
- Deactivates venv on exit

Usage:
  bash start.sh

Updated README with new recommended startup method.

README.md

@@ -35,18 +35,34 @@ A modern digital signage player built with Kivy framework that displays content
 
 ## Usage
 
-### Manual Start
+### Recommended: Using Start Script (with Virtual Environment)
 ```bash
-cd src
-python3 main.py
+chmod +x start.sh
+./start.sh
 ```
+This script automatically:
+- Activates the Python virtual environment
+- Checks for configuration
+- Starts the player
 
-### Using Run Script
+### Alternative: Using Run Script
 ```bash
 chmod +x run_player.sh
 ./run_player.sh
 ```
 
+### Manual Start
+```bash
+# With virtual environment
+source .venv/bin/activate
+cd src
+python3 main.py
+
+# Without virtual environment
+cd src
+python3 main.py
+```
+
 ## Controls
 
 - **Mouse/Touch Movement**: Shows control panel for 3 seconds