Clear release notes (#441)

Author: shsms

RELEASE_NOTES.md

@@ -2,14 +2,16 @@
 
 ## Summary
 
-This release introduces the experimental `GroupingLatestValueCache` and includes a couple of bug fixes.
+<!-- Here goes a general summary of what this release is about -->
+
+## Upgrading
+
+<!-- Here goes notes on how to upgrade from previous versions, including deprecations and what they should be replaced with -->
 
 ## New Features
 
-- This release introduces the experimental `GroupingLatestValueCache`.  It is similar to the `LatestValueCache`, but accepts an additional key-function as an argument, which takes each incoming message and returns a key for that message.  The latest value received for each unique key gets cached and is available to look up on-demand through a `collections.abc.Mapping` interface.
+<!-- Here goes the main new features and examples or instructions on how to use them -->
 
 ## Bug Fixes
 
-- Any open calls to `NopReceiver.ready()` now return as soon as the receiver is closed.
-
-- The `__str__` representation of broadcast receivers now include the receiver's name.
+<!-- Here goes notable bug fixes that are worth a special mention or explanation -->