Add RELEASE.txt entry for compound performance regression fix (HDFGro…

…up#3376) (HDFGroup#3416)

release_docs/RELEASE.txt

@@ -292,6 +292,16 @@ Bug Fixes since HDF5-1.14.0 release
 ===================================
     Library
     -------
+    - Fixed performance regression with some compound type conversions
+33
+      In-place type conversion was introduced for most use cases in 1.14.2.
+      While being able to use the read buffer for type conversion potentially
+      improves performance by performing the entire I/O at once, it also
+      disables the optimized compound type conversion used when the destination
+      is a subset of the source. Disabled in-place type conversion when using
+      this optimized conversion and there is no benefit in terms of the I/O
+      size.
+
     - Fixed an assertion in a previous fix for CVE-2016-4332
 
       An assert could fail when processing corrupt files that have invalid