Clear release notes (frequenz-floss#1181)

Author: shsms

RELEASE_NOTES.md

@@ -2,18 +2,16 @@
 
 ## Summary
 
-## New Features
-
-- Add a `stop()` method to the `FormulaEngine`. Now it is possible to stop custom formulas.
+<!-- Here goes a general summary of what this release is about -->
 
-- Stop fallback formulas when primary formula starts working again.
+## Upgrading
 
-## Bug Fixes
+<!-- Here goes notes on how to upgrade from previous versions, including deprecations and what they should be replaced with -->
 
-- Fixed a bug with formulas raising exception when stopped.
+## New Features
 
-- Fixed a bug that raised `CancelledError` when actor was started with `frequenz.sdk.actor.run` and stopped.
+<!-- Here goes the main new features and examples or instructions on how to use them -->
 
-- Stop catching `BaseException` in `frequenz.sdk.actor.run`. Only `CancelledError` and `Exception` are caught now.
+## Bug Fixes
 
 - Fix `MetricFetcher` leaks when a requested metric fetcher already existed.