Add environment variable configuration support

- Add .env.example file with API key placeholders
- Update README.md with .env file setup instructions
- Add dotenv loading in main.py for environment variables

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

.env.example

@@ -0,0 +1,2 @@
+ALPHA_VANTAGE_API_KEY=alpha_vantage_api_key_placeholder
+OPENAI_API_KEY=openai_api_key_placeholder

README.md

@@ -124,6 +124,12 @@ You will need the OpenAI API for all the agents.
 export OPENAI_API_KEY=$YOUR_OPENAI_API_KEY
 ```
 
+Alternatively, you can create a `.env` file in the project root with your API keys (see `.env.example` for reference):
+```bash
+cp .env.example .env
+# Edit .env with your actual API keys
+```
+
 ### CLI Usage
 
 You can also try out the CLI directly by running:

main.py

@@ -1,6 +1,11 @@
 from tradingagents.graph.trading_graph import TradingAgentsGraph
 from tradingagents.default_config import DEFAULT_CONFIG
 
+from dotenv import load_dotenv
+
+# Load environment variables from .env file
+load_dotenv()
+
 # Create a custom config
 config = DEFAULT_CONFIG.copy()
 config["llm_provider"] = "google"  # Use a different model