Decode cache data to the correct endpoint type

Use the return annotation to decode cached data to the correct type.
This follows the same logic FastAPI uses to JSON request bodies.

For the PickleCoder, this is a no-op as pickle already stores type
information in the serialised data.

README.md

@@ -101,6 +101,30 @@ key_builder | which key builder to use, default to builtin
 
 You can also use `cache` as decorator like other cache tools to cache common function result.
 
+
+### Supported data types
+
+When using the (default) `JsonCoder`, the cache can store any data type that FastAPI can convert to JSON, including Pydantic models and dataclasses,
+_provided_ that your endpoint has a correct return type annotation, unless
+the return type is a standard JSON-supported type such as a dictionary or a list.
+
+E.g. for an endpoint that returns a Pydantic model named `SomeModel`:
+
+```python
+from .models import SomeModel, create_some_model
+
+@app.get("/foo")
+@cache(expire=60)
+async def foo() -> SomeModel:
+    return create_some_model
+```
+
+It is not sufficient to configure a response model in the route decorator; the cache needs to know what the method itself returns.
+
+If no return type decorator is given, the primitive JSON type is returned instead.
+
+For broader type support, use the `fastapi_cache.coder.PickleCoder` or implement a custom coder (see below).
+
 ### Custom coder
 
 By default use `JsonCoder`, you can write custom coder to encode and decode cache result, just need