Release notes update after release v0.7.0 (#82)

Author: flora-hofmann-frequenz

RELEASE_NOTES.md

@@ -1,7 +1,17 @@
 # Frequenz Reporting API Client 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
 
-* TLS is now enabled for all connections.
+<!-- 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 -->