Add release note for assumes now recognizing class-like FP tests

Author: arsenm

llvm/docs/ReleaseNotes.rst

@@ -102,9 +102,12 @@ Changes to TableGen
 * Named arguments are supported. Arguments can be specified in the form of
   ``name=value``.
 
-Changes to Interprocedural Optimizations
+Changes to Optimizations
 ----------------------------------------
 
+* :ref:`llvm.assume <int_assume>` now recognizes certain
+  floating-point tests. e.g. ``__builtin_assume(!isnan(x))``
+
 Changes to the AArch64 Backend
 ------------------------------