📝 Update release notes

docs/release-notes.md

@@ -1,5 +1,13 @@
 ## Latest changes
 
+* Improve handling of custom classes for `Request`s and `APIRoute`s.
+    * This helps to more easily solve use cases like:
+        * Reading a body before and/or after a request (equivalent to a middleware).
+        * Run middleware-like code only for a subset of *path operations*.
+        * Process a request before passing it to a *path operation function*. E.g. decompressing, deserializing, etc.
+        * Processing a response after being generated by *path operation functions* but before returning it. E.g. adding custom headers, logging, adding extra metadata.
+    * New docs section: [Custom Request and APIRoute class](https://fastapi.tiangolo.com/tutorial/custom-request-and-route/).
+    * PR [#589](https://github.com/tiangolo/fastapi/pull/589) by [@dmontagu](https://github.com/dmontagu).
 * Fix preserving custom route class in routers when including other sub-routers. PR [#538](https://github.com/tiangolo/fastapi/pull/538) by [@dmontagu](https://github.com/dmontagu).
 
 ## 0.40.0