DOCSP-45881: Parallel operations admonition (#160)

Author: norareidy

source/fundamentals/transactions.txt

@@ -159,6 +159,15 @@ If you require more control over your transactions, see the `ClientSession API
 documentation <{+api+}/struct.ClientSession.html#transactions>`__
 to find an example that shows how to manually create and commit a transaction.
 
+.. sharedinclude:: dbx/transactions-parallelism.rst
+
+   .. replacement:: driver-specific-content
+
+      If you're using {+server+} v8.0 or later, you can perform
+      write operations on multiple namespaces within a single transaction by using
+      bulk write operations. For more information, see the :ref:`<rust-bulk-guide>`
+      guide.
+
 Additional Information
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