Update docs sample code (#158)

Author: SimonCao1207

docs/usage.md

@@ -14,7 +14,7 @@ Here are a few examples of how to use SWE-ReX.
 ```python
 import asyncio
 from swerex.deployment.local import LocalDeployment
-from swerex.runtime.abstract import CreateSessionRequest, BashAction, Command
+from swerex.runtime.abstract import CreateBashSessionRequest, BashAction, Command
 
 deployment = LocalDeployment()
 
@@ -27,7 +27,7 @@ async def run_some_stuff(deployment):
     print(await runtime.execute(Command(command=["echo", "Hello, world!"])))
 
     # Create a bash session
-    await runtime.create_session(CreateSessionRequest())
+    await runtime.create_session(CreateBashSessionRequest())
 
     # Run a command in the session
     # The difference to the one-off commands is that environment state persists!
@@ -81,4 +81,4 @@ So what's going on here? There's multiple steps:
 
 ## Running with modal
 
-...
+...