Refactor model API key documentation (#3)

Consolidate model API key section for clarity.

Author: pirate

README.md

@@ -235,16 +235,8 @@ Create a `.env` file in your project root:
 BROWSERBASE_API_KEY=your_browserbase_api_key_here
 BROWSERBASE_PROJECT_ID=your_browserbase_project_id_here
 
-# Model API key (at least one required, checked in this order)
-MODEL_API_KEY=your_api_key                          # Generic override (highest priority)
-OPENAI_API_KEY=your_openai_key                      # OpenAI
-ANTHROPIC_API_KEY=your_anthropic_key                # Anthropic (Claude)
-GOOGLE_GENERATIVE_AI_API_KEY=your_gemini_key        # Google Gemini
-AZURE_API_KEY=your_azure_key                        # Azure OpenAI
-MISTRAL_API_KEY=your_mistral_key                    # Mistral
-GROQ_API_KEY=your_groq_key                          # Groq
-CEREBRAS_API_KEY=your_cerebras_key                  # Cerebras
-DEEPSEEK_API_KEY=your_deepseek_key                  # DeepSeek
+# Model API key
+MODEL_API_KEY=your_api_key                          # OpenAI, Anthropic, Gemini, etc. key
 
 # Optional: Custom API URLs
 STAGEHAND_API_URL=https://api.stagehand.browserbase.com/v1  # Stagehand API (default)