CPP: Add change note.

Author: geoffw0

change-notes/1.21/analysis-cpp.md

@@ -12,6 +12,7 @@
 | **Query**                  | **Expected impact**    | **Change**                                                       |
 |----------------------------|------------------------|------------------------------------------------------------------|
 | Mismatching new/free or malloc/delete (`cpp/new-free-mismatch`) | Fewer false positive results | Fixed an issue where functions were being identified as allocation functions inappropriately.  Also affects `cpp/new-array-delete-mismatch` and `cpp/new-delete-array-mismatch`. |
+| Overflow in uncontrolled allocation size (`cpp/uncontrolled-allocation-size`) | More correct results | This query has been reworked so that it can find a wider variety of results. |
 | Resource not released in destructor (`cpp/resource-not-released-in-destructor`) | Fewer false positive results | Resource allocation and deallocation functions are now determined more accurately. |
 
 ## Changes to QL libraries