Changelog: add explanation r. QLoRA mem savings

CHANGELOG.md

@@ -1,5 +1,13 @@
 ### 0.43.2
 
+This release is quite significant as the QLoRA bug fix big implications for higher `seqlen` and batch sizes.
+
+For each sequence (i.e. batch size increase of one) we expect memory savings of:
+- 405B: 39GB for seqlen 1024, and 4888GB for 128k
+- 70B: 20.1GB for 1024 and 2516GB for 128k
+
+This was due to activations being unnecessary for frozen parameters, yet the memory for them was still erroneously allocated due to the now fixed bug.
+
 #### Improvements:
 
 - docs: FSDP+QLoRA and CPU install guide (#1211 #1227, thanks @stevhliu)