DOCSP-4079: GridFS write concern (#547)

* DOCSP-4079: GridFS write concern

* fix

* format

* tech review

(cherry picked from commit 911e639)

source/fundamentals/gridfs.txt

@@ -133,6 +133,16 @@ following code snippet:
 See the `GridFSUploadOptions <{+api+}/apidocs/mongodb-driver-core/com/mongodb/client/gridfs/model/GridFSUploadOptions.html>`__
 API Documentation for more information.
 
+.. important:: Use a ``MAJORITY`` Write Concern
+
+   When storing files in a GridFS bucket, ensure that you use the ``WriteConcern.MAJORITY``
+   write concern. If you specify a different write concern, replica set elections that occur
+   during a GridFS file upload might interrupt the upload process and cause some file chunks
+   to be lost.
+
+   For more information about write concerns, see the :manual:`Write Concern </reference/write-concern/>`
+   page in the Server manual.
+
 Upload a File Using an Input Stream
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~