Enhance configuration to support loading IMAP password and OpenRouter API key from files, and update README with new settings

config.yaml.example

@@ -2,14 +2,14 @@ imap:
   server: "imap.gmail.com"  # Example for Gmail
   port: 993
   username: "your-email@gmail.com"
-  password: "${IMAP_PASSWORD}"  # Will be read from environment variable
+  password: "${IMAP_PASSWORD}"  # From environment variable, or use "file:///path/to/password.txt"
   mailbox_in: "INBOX"
   draft_box: "Drafts"
   processed_box: "Processed"  # Folder where processed emails will be moved
   use_tls: true
 
 ai:
-  openrouter_api_key: "${OPENROUTER_API_KEY}"  # Will be read from environment variable
+  openrouter_api_key: "${OPENROUTER_API_KEY}"  # From environment variable, or use "file:///path/to/api-key.txt"
   model: "anthropic/claude-2"  # Other options: "openai/gpt-4", "google/palm-2"
   temperature: 0.7  # 0.0 to 1.0, lower for more focused responses
   max_tokens: 2000  # Adjust based on your needs and model limits