Update release notes for the v0.1.0 release (#6)

Author: llucax

RELEASE_NOTES.md

@@ -1,17 +1,5 @@
 # Frequenz Filter Lines Superfence 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
-
-<!-- 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 -->
+This is the first release of this extension, a superfence for
+[pymdown-extensions](https://github.com/facelessuser/pymdown-extensions) to
+filter code block lines.