Prepare readme for release (#82)

Author: llucax

RELEASE_NOTES.md

@@ -1,19 +1,10 @@
 # Frequenz Microgrid API Client Release Notes
 
-## Summary
-
-<!-- Here goes a general summary of what this release is about -->
-
 ## Upgrading
 
 - This release stops using `betterproto` and `grpclib` as backend for gRPC and goes back to using Google's `grpcio` and `protobuf`.
 
     If your code was using `betterproto` and `grpclib`, it now needs to be ported to use `grpcio` and `protobuf` too. Remember to also remove any `betterproto` and `grpclib` dependencies from your project.
 
-## New Features
-
-<!-- Here goes the main new features and examples or instructions on how to use them -->
-
-## Bug Fixes
+- We are now using base-client v0.6.0.
 
-<!-- Here goes notable bug fixes that are worth a special mention or explanation -->