DOCSP-38359 -- Add SEO content to reference.txt (#908)

* DOCSP-38359 -- Add SEO content to reference.txt

* DOCSP-38359 -- add source constant

* DOCSP-38359 -- typo fix

Author: jvincent-mongodb

source/reference.txt

@@ -12,8 +12,21 @@ Reference
    :depth: 1
    :class: singlecol
 
+
+To create or update a |cloud| or |mms-full| cluster with the {+mcli+}, 
+you must provide cluster configuration properties with a ``.yaml`` 
+or ``.json`` file.  
+
+Section Overview
+----------------
+
+:ref:`Cluster Configuration File <mms-cluster-settings-file>`
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Learn about the :ref:`mms-config-props` that are required for 
+creating or updating a cluster.
+
 .. toctree::
    :titlesonly:
 
    /reference/mms-cluster-settings-file
-