Undo DOCSP-45737 (#134)

Author: mcmorisi

source/write/bulk-write.txt

@@ -69,8 +69,9 @@ To insert multiple documents, create an instance of ``InsertOne`` for each docum
 
 .. note::
 
-   You must specify a value for the ``_id`` field for each document you insert. If you don't,
-   the driver throws a ``DuplicateKeyError``.
+   Duplicate ``_id`` values violate unique index constraints, which causes the
+   driver to return a ``DuplicateKeyError``. To avoid this error, ensure that
+   each document you insert has a unique ``_id`` value.
 
 Update Operations
 ~~~~~~~~~~~~~~~~~