Clear release notes (#367)

Author: shsms

RELEASE_NOTES.md

@@ -1,5 +1,17 @@
 # Frequenz channels Release Notes
 
+## Summary
+
+<!-- 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
 
-- Added a `Receiver.close()` method for closing just a receiver.  Also implemented it for all the `Receiver` implementations in this library.
+<!-- Here goes the main new features and examples or instructions on how to use them -->
+
+## Bug Fixes
+
+<!-- Here goes notable bug fixes that are worth a special mention or explanation -->