update readme

- updated readme to mention .env
- added model arg back

README.md

@@ -15,9 +15,9 @@ For a quick demonstration see my [demo video on twitter](https://twitter.com/bio
     pip install -r requirements.txt
     cp .env.sample .env
 
-Add your openAI api key to `.env` 
+Add your openAI api key to `.env` - _warning!_ by default this uses GPT-4 and may make many repeated calls to the api.
 
-_warning!_ By default wolverine uses GPT-4 and may make many repeated calls to the api.
+    OPENAI_API_KEY=sk-abcdefghijklmopqrstuvwxyz
 
 ## Example Usage
 
@@ -29,6 +29,10 @@ You can also run with other models, but be warned they may not adhere to the edi
 
     python wolverine.py --model=gpt-3.5-turbo buggy_script.py "subtract" 20 3
 
+If you want to use GPT-3.5 by default instead of GPT-4 add this to `.env`:
+
+    DEFAULT_MODEL=gpt-3.5-turbo
+
 ## Future Plans
 
 This is just a quick prototype I threw together in a few hours. There are many possible extensions and contributions are welcome: