Add RELEASE_NOTES entries

Signed-off-by: Sahas Subramanian <[email protected]>

Author: shsms

RELEASE_NOTES.md

@@ -9,13 +9,15 @@
 <!-- Here goes notes on how to upgrade from previous versions, including deprecations and what they should be replaced with -->
 
 - `Channels` has been upgraded to version 0.16.0, for information on how to upgrade visit https://github.com/frequenz-floss/frequenz-channels-python/releases/tag/v0.16.0
+- `Quantity` objects are no longer hashable.  This is because of the pitfalls of hashing `float` values.
 
 ## New Features
 
 - Add `abs()` support for quantities.
 - Add quantity class `Frequency` for frequency values.
 - Quantities can now be multiplied with `Percentage` types.
-- `FormulaEngine` arithmetics now supports scalar multiplication with floats and addition with Quantities
+- `FormulaEngine` arithmetics now supports scalar multiplication with floats and addition with Quantities.
+- Add a `isclose()` method on quantities to compare them to other values of the same type.  Because `Quantity` types are just wrappers around `float`s, direct comparison might not always be desirable.
 
 ## Bug Fixes