Clear release notes (#512)

Author: shsms

RELEASE_NOTES.md

@@ -1,12 +1,17 @@
 # Frequenz channels Release Notes
 
+## Summary
+
+<!-- Here goes a general summary of what this release is about -->
+
 ## Upgrading
 
-- `LatestValueCache` now closes the receiver when it is stopped.
-- Fetching values from stopped `LatestValueCache` instances is now disallowed.
+<!-- Here goes notes on how to upgrade from previous versions, including deprecations and what they should be replaced with -->
 
 ## New Features
 
-- There's a new `Oneshot` channel, which returns a sender and a receiver.  A single message can be sent using the sender, after which it will be closed.  And the receiver will close as soon as the message is received.
+<!-- Here goes the main new features and examples or instructions on how to use them -->
+
+## Bug Fixes
 
-- `Sender`s now have an `aclose`, which must be called, when they are no-longer needed.
+<!-- Here goes notable bug fixes that are worth a special mention or explanation -->