docs: Update README and add Linux setup script

Improve documentation and add a setup script for easy deployment on Linux systems.

- Update README.md with instructions for the new multi-voice slash commands and the oices/ directory structure.
- Add a comprehensive 'Linux Server Deployment' section to the README, detailing both a quick setup via a new script and a manual systemd service setup.
- Create setup_linux.sh to automate dependency checking, virtual environment creation, and service installation on Linux.
- Revise comments in .env.example for clarity and to reflect the latest configuration options.

.env.example

@@ -1,9 +1,16 @@
-# Discord Bot Token (from Discord Developer Portal)
-DISCORD_TOKEN=your_discord_bot_token_here
+# Discord Bot Configuration
+# Copy this file to .env and fill in your values
 
-# Channel ID to monitor for TTS messages
-# Right-click the channel in Discord and copy ID (enable Developer Mode in settings)
+# Your Discord bot token (from Discord Developer Portal)
+DISCORD_TOKEN=your_bot_token_here
+
+# The text channel ID to monitor for messages
+# (Right-click channel with Developer Mode enabled -> Copy ID)
 TEXT_CHANNEL_ID=123456789012345678
 
-# Path to the voice reference WAV file for voice cloning
-VOICE_WAV_PATH=./voice.wav
+# Directory containing voice .wav files
+VOICES_DIR=./voices
+
+# Default voice name (optional - uses first found voice if not set)
+# This should match the filename without .wav extension (case-insensitive)
+# DEFAULT_VOICE=masterchief