chore(docs): use environment variables for authentication in code snippets

Author: stainless-app[bot]

README.md

@@ -102,14 +102,15 @@ pip install runloop_api_client[aiohttp]
 Then you can enable it by instantiating the client with `http_client=DefaultAioHttpClient()`:
 
 ```python
+import os
 import asyncio
 from runloop_api_client import DefaultAioHttpClient
 from runloop_api_client import AsyncRunloop
 
 
 async def main() -> None:
     async with AsyncRunloop(
-        bearer_token="My Bearer Token",
+        bearer_token=os.environ.get("RUNLOOP_API_KEY"),  # This is the default and can be omitted
         http_client=DefaultAioHttpClient(),
     ) as client:
         devbox_view = await client.devboxes.create()