Clear release notes (#117)

Author: shsms

RELEASE_NOTES.md

@@ -1,5 +1,17 @@
 # Frequenz Microgrid API Client Release Notes
 
+## Summary
+
+<!-- Here goes a general summary of what this release is about -->
+
 ## Upgrading
 
-- Widen `frequenz-client-base` dependency to allow `v0.9.0`.
+<!-- Here goes notes on how to upgrade from previous versions, including deprecations and what they should be replaced with -->
+
+## New Features
+
+<!-- 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 -->