DOCSP-20890 Add readPreference example (#254)

* DOCSP-20890 Add readPreference example

* DOCSP-20890 updates for feedback

Author: kanchana-mongodb

source/reference/format/data-lake-configuration.txt

@@ -570,6 +570,39 @@ The {+data-lake-short+} configuration has the following format:
          </core/read-preference/>`, which describes how to route read 
          requests to the cluster.
 
+         .. example:: 
+
+            The following ``readPreference`` setting specifies ``secondary`` :manual:`mode </core/read-preference/#std-label-read-pref-modes-summary>` 
+            and ``ANALYTICS`` :atlas:`nodeType </reference/replica-set-tags/#node-types>`.
+
+            .. code-block:: json 
+               :copyable: false 
+               :emphasize-lines: 9-20
+
+               { 
+                 ... 
+                 "stores": [
+                   {
+                     "provider": "atlas",
+                     "clusterName": <CLUSTER_NAME>,
+                     "name": <STORE_NAME>,
+                     "projectId": <PROJECT_ID>,
+                     "readPreference": {
+                       "mode": "secondary",
+                       "tagSets": [
+                         [
+                           {
+                             "name": "nodeType",
+                             "value": "ANALYTICS"
+                           }
+                         ],
+                         ...
+                       ]
+                     }
+                   }
+                 ]
+               }
+
       .. datalakeconf:: stores.[n].readPreference.mode 
 
          *Optional.* :manual:`Read preference mode 
@@ -595,7 +628,7 @@ The {+data-lake-short+} configuration has the following format:
 
       .. datalakeconf:: stores.[n].readPreference.maxStalenessSeconds
 
-         *Optional.* Maximum replication lag, or “staleness”, for reads 
+         *Optional.* Maximum replication lag, or "staleness", for reads 
          from secondaries. To learn more about ``maxStalenessSeconds``, 
          see :manual:`Read Preference maxStalenessSeconds 
          </core/read-preference-staleness/>`.