Fix typo in type checking note (#518)

docs/agents.md

@@ -251,7 +251,7 @@ PydanticAI is designed to work well with static type checkers, like mypy and pyr
 
     That said, because PydanticAI uses Pydantic, and Pydantic uses type hints as the definition for schema and validation, some types (specifically type hints on parameters to tools, and the `result_type` arguments to [`Agent`][pydantic_ai.Agent]) are used at runtime.
 
-    We (the library developers) have messed up if type hints are confusing you more than they're help you, if you find this, please create an [issue](https://github.com/pydantic/pydantic-ai/issues) explaining what's annoying you!
+    We (the library developers) have messed up if type hints are confusing you more than helping you, if you find this, please create an [issue](https://github.com/pydantic/pydantic-ai/issues) explaining what's annoying you!
 
 In particular, agents are generic in both the type of their dependencies and the type of results they return, so you can use the type hints to ensure you're using the right types.