docs: add comprehensive testing and Discord bot setup guide

Co-authored-by: aider (openai/unsloth/Qwen3-Coder-Next) <aider@aider.chat>

DISCORD_BOT_TOKEN=your_bot_token_here

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+
+Alternatively, set the environment variable in your system:
+- On Linux/macOS: `export DISCORD_BOT_TOKEN=your_bot_token_here`
+- On Windows: `set DISCORD_BOT_TOKEN=your_bot_token_here`
+
+## Step 5: Test the Application
+
+1. Start the bot:
+   ```bash
+   python app.py
+   ```
+
+2. You should see a message like:
+   ```
+   YourBotName#1234 has connected to Discord!
+   ```
+
+## Step 6: Test Receipt Upload
+
+1. Open Discord and find your bot in a server where it's added
+2. Send a message with a PDF receipt attached
+3. The bot should:
+   - Save the PDF to the `receipts/` folder
+   - Extract text from the PDF
+   - Parse the receipt data
+   - Add it to the database
+   - Send a confirmation message
+
+## Step 7: Test Commands
+
+### Add a Receipt Manually
+
+Use the command: