Update release notes

Signed-off-by: Elzbieta Kotulska <[email protected]>

Author: ela-kotulska-frequenz

RELEASE_NOTES.md

@@ -42,6 +42,8 @@
 
 - Classes `Bounds` and `SystemBounds` now implement the `__contains__` method, allowing the use of the `in` operator to check whether a value falls within the bounds or not.
 
+- Fallback components are used in generated formulas. If primary components is unavailable, formula will generate metric from fallback components.
+
 ## Enhancements
 
 - The resampler now shows an error message where it is easier to identify the component and metric when it can't find relevant data for the current resampling window.