DOCS-14888 setFeatureCompatibilityVersion wtimeout

source/reference/command/setFeatureCompatibilityVersion.txt

@@ -15,10 +15,6 @@ Definition
 
 .. dbcommand:: setFeatureCompatibilityVersion
 
-   .. versionadded:: 3.4
-
-   .. versionchanged:: 3.6
-
    Enables or disables the features that persist data incompatible with
    earlier versions of MongoDB. You can only issue the
    :dbcommand:`setFeatureCompatibilityVersion` against the ``admin``
@@ -28,7 +24,10 @@ Definition
 
    .. code-block:: javascript
 
-      db.adminCommand( { setFeatureCompatibilityVersion: <version> } )
+      db.adminCommand( {
+         setFeatureCompatibilityVersion: <version>,
+         writeConcern: { wtimeout: <timeout> }
+      } )
 
    The values for the ``version`` are:
 
@@ -104,6 +103,18 @@ Definition
           Disables the :ref:`3.4 features that persist data
           incompatible with MongoDB 3.2 <3.4-compatibility-enabled>`.
 
+   The optional ``writeConcern`` specifies the write concern
+   :ref:`wc-wtimeout` value in milliseconds:
+
+   - The time period that the :term:`primary` waits for
+     acknowledgment from the majority of the replica set members. If the
+     acknowledgment is not received in the time period, the operation
+     fails.
+
+   - Default is ``60000`` milliseconds. Use a longer time period if the
+     :term:`secondary` members of the replica set have a delay that
+     exceeds the :ref:`wc-wtimeout` default.
+
    .. note::
 
       .. include:: /includes/list-run-command-targets.rst
@@ -434,3 +445,23 @@ Set Feature Compatibility Version on MongoDB 3.4 Deployments
                If performed as part of a downgrade to 3.2 procedure, you must also
                manually remove the existing usage before downgrading the binaries. For
                details, see :ref:`3.4-downgrade-features-prereq`.
+
+Set Write Concern Timeout
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The following example sets the optional write concern :ref:`wc-wtimeout`
+field to 5000 (5 seconds).
+
+.. note::
+
+   Run the :dbcommand:`setFeatureCompatibilityVersion` command against
+   the ``admin`` database.
+
+   .. include:: /includes/list-run-command-targets.rst
+
+.. code-block:: javascript
+
+   db.adminCommand( {
+      setFeatureCompatibilityVersion: "4.2",
+      writeConcern: { wtimeout: 5000 }
+   } )