Add Release Notes

Author: Maetveis

clang/docs/ReleaseNotes.rst

@@ -326,6 +326,16 @@ Improvements to Clang's diagnostics
 - Now correctly diagnose a tentative definition of an array with static
   storage duration in pedantic mode in C. (#GH50661)
 
+- ``-Whigher-precisision-for-complex-divison`` no longer incorrectly warns when the divisor is real
+  in complex division. (#GH131127)
+
+- ``-Whigher-precisision-for-complex-divison`` now correctly warns when (#GH131127):
+
+  - The dividend is real, but the divisor is complex.
+  - When the complex division happens in a higher precision type than the dividend due to arithmetic promotion.
+  - When using the divide and assign operator (``/=``)
+  
+
 Improvements to Clang's time-trace
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