Clear release notes (#364)

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 support for disabling the overflow-warning log messagess in broadcast receivers, through the `warn_on_overflow` parameter on `Broadcast.new_receiver()` calls.
+<!-- 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 -->