[DOCSP-26701] Add 4.12.1 admonition (#460)

* add 4.12.1 update

* Apply suggestions from code review

Co-authored-by: Rea Rustagi <[email protected]>

Co-authored-by: Rea Rustagi <[email protected]>

Author: mongoKart

source/whats-new.txt

@@ -33,6 +33,11 @@ Learn what's new in:
 What's New in 4.12
 ------------------
 
+.. important:: Upgrade Driver to Version 4.12.1
+
+   The 4.12.1 {+driver-short+} includes a fix to a regression in monitoring logic
+   that could cause processes to crash.
+
 New features of the 4.12 {+driver-short+} release include:
 
 - Redefinition of the ``ChangeStream`` class as an async iterable.