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.

start.sh

@@ -0,0 +1,58 @@
+#!/bin/bash
+
+# Kivy Signage Player Startup Script
+# This script activates the virtual environment and starts the player
+
+# Get the directory where this script is located
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+
+echo "=========================================="
+echo "Starting Kivy Signage Player"
+echo "=========================================="
+echo ""
+
+# Change to the project directory
+cd "$SCRIPT_DIR"
+echo "Project directory: $SCRIPT_DIR"
+
+# Check if virtual environment exists
+if [ -d ".venv" ]; then
+    echo "Activating virtual environment..."
+    source .venv/bin/activate
+    echo "✓ Virtual environment activated"
+else
+    echo "Warning: Virtual environment not found at .venv/"
+    echo "Creating virtual environment..."
+    python3 -m venv .venv
+    source .venv/bin/activate
+    echo "Installing dependencies..."
+    pip3 install -r requirements.txt
+    echo "✓ Virtual environment created and dependencies installed"
+fi
+
+echo ""
+
+# Check if configuration exists
+if [ ! -f "config/app_config.txt" ]; then
+    echo "=========================================="
+    echo "⚠ WARNING: Configuration file not found!"
+    echo "=========================================="
+    echo ""
+    echo "Please configure the player before running:"
+    echo "  1. Copy config/app_config.txt.example to config/app_config.txt"
+    echo "  2. Edit the configuration file with your server details"
+    echo ""
+    read -p "Press Enter to continue anyway, or Ctrl+C to exit..."
+    echo ""
+fi
+
+# Change to src directory and start the application
+echo "Starting application..."
+echo "=========================================="
+echo ""
+
+cd src
+python3 main.py
+
+# Deactivate virtual environment when app exits
+deactivate