Update .env.example with Docker configuration

Add Docker-specific paths and documentation
Include all required API keys and MCP ports
Show default values for optional settings

.env.example

@@ -1,13 +1,25 @@
-OPENAI_API_BASE=""
-OPENAI_API_KEY=""
-ALPHAADVANTAGE_API_KEY =""
-JINA_API_KEY=""
+# =============================================================================
+# AI-Trader Environment Configuration
+# =============================================================================
+# Copy this file to .env and fill in your actual values
+# Docker Compose automatically reads .env from project root
 
+# AI Model API Configuration
+OPENAI_API_BASE=https://your-openai-proxy.com/v1
+OPENAI_API_KEY=your_openai_key_here
+
+# Data Source Configuration
+ALPHAADVANTAGE_API_KEY=your_alphavantage_key_here
+JINA_API_KEY=your_jina_key_here
+
+# System Configuration (Docker default paths)
+RUNTIME_ENV_PATH=/app/data/runtime_env.json
+
+# MCP Service Ports (defaults shown)
 MATH_HTTP_PORT=8000
 SEARCH_HTTP_PORT=8001
 TRADE_HTTP_PORT=8002
 GETPRICE_HTTP_PORT=8003
 
+# Agent Configuration
 AGENT_MAX_STEP=30
-
-RUNTIME_ENV_PATH = ""