Prepare release notes for v1.0.0-rc2212 (#1457)

Author: llucax

RELEASE_NOTES.md

@@ -1,15 +1,9 @@
 # Frequenz Python SDK Release Notes
 
-## Summary
-
-<!-- Here goes a general summary of what this release is about -->
-
 ## Upgrading
 
 - Custom validators passed through a configuration dataclass field's `metadata` (as used by `load_config()` and `ConfigManager.new_receiver()`) must now raise a `marshmallow.ValidationError` to reject a value. `marshmallow` 4 removed support for validators that signal failure by returning `False`, so such validators are now ignored and the invalid value is accepted silently. This affects you as soon as `marshmallow` 4 is installed, which `frequenz-quantities` 1.0.2 and later require.
 
-<!-- Here goes notes on how to upgrade from previous versions, including deprecations and what they should be replaced with -->
-
 ## New Features
 
 * Added `SteamBoilerPool` for monitoring and controlling pools of steam boilers, available via `microgrid.new_steam_boiler_pool()`.