move bc into an admonition

Author: rustagir

source/whats-new.txt

@@ -35,6 +35,24 @@ following versions of the {+php-library+}:
 What's New in 2.0
 -----------------
 
+.. important:: Breaking Changes
+
+   The {+library-short+} v2.0 release introduces the following breaking
+   changes:
+
+   - The following methods return ``void`` instead of the raw command
+     response:
+   
+     - ``MongoDB\\Client``: ``dropDatabase()``
+     - ``MongoDB\\Collection``: ``drop()``, ``dropIndex()``,
+       ``dropIndexes()``, ``dropSearchIndex()``, ``rename()``
+     - ``MongoDB\\Database``: ``createCollection()``, ``drop()``,
+       ``dropCollection()``, ``renameCollection()``
+   
+   To learn more about breaking changes in this release, see the
+   :ref:`Version 2.0 Breaking Changes <php-v2-breaking-changes>` section
+   in the Upgrade Library Versions guide.
+
 The {+library-short+} v2.0 release includes the following features,
 improvements, and fixes:
 
@@ -75,19 +93,6 @@ improvements, and fixes:
   </reference/map-reduce-to-aggregation-pipeline/>` in the
   {+mdb-server+} manual.
 
-- The following methods return ``void`` instead of the raw command
-  response:
-
-  - ``MongoDB\\Client``: ``dropDatabase()``
-  - ``MongoDB\\Collection``: ``drop()``, ``dropIndex()``,
-    ``dropIndexes()``, ``dropSearchIndex()``, ``rename()``
-  - ``MongoDB\\Database``: ``createCollection()``, ``drop()``,
-    ``dropCollection()``, ``renameCollection()``
-
-  To learn more about this breaking change, see the :ref:`Version 2.0
-  Breaking Changes <php-v2-breaking-changes>` section in the Upgrade
-  Library Versions guide.
-
 .. _php-lib-version-1.20:
 
 What's New in 1.20