Update release notes

Signed-off-by: Leandro Lucarella <[email protected]>

Author: llucax

RELEASE_NOTES.md

@@ -1,29 +1,8 @@
 # Frequenz Repository Configuration 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 -->
-
-### Cookiecutter template
-
-<!-- Here upgrade steps for cookiecutter specifically -->
-
-## New Features
-
-<!-- Here goes the main new features and examples or instructions on how to use them -->
-
-### Cookiecutter template
-
-<!-- Here new features for cookiecutter specifically -->
-
 ## Bug Fixes
 
-<!-- Here goes notable bug fixes that are worth a special mention or explanation -->
-
-### Cookiecutter template
+- Pin `sybil` to < 6.1
 
-<!-- Here bug fixes for cookiecutter specifically -->
+    Sybil 6.1.0 fixes a bug which we thought it was proper behavior, so
+    upgrading to it would break our tests.