DOCS-13479 Add note for 5.1 out and merge behavior on RS

Author: ianf-mongodb

source/reference/operator/aggregation/merge.txt

@@ -46,14 +46,14 @@ Definition
        information, see :ref:`merge-behavior-same-collection`.
 
      - Pipelines with the :pipeline:`$merge` stage can run on 
-       ``replica set secondary nodes`` if all the nodes in cluster have 
+       replica set secondary nodes if all the nodes in cluster have 
        :ref:`featureCompatibilityVersion <view-fcv>` set 
        to ``4.4`` or higher and the :doc:`/core/read-preference`
        allows secondary reads. 
 
        - Read operations of the :pipeline:`$merge` statement are sent to 
-         ``secondary`` nodes, while the write operations occur only on the 
-         ``primary`` nodes.
+         secondary nodes, while the write operations occur only on the 
+         primary node.
 
        - Not all driver versions support targeting of :pipeline:`$merge` 
          operations to replica set secondary nodes. Check your 

source/reference/operator/aggregation/out.txt

@@ -155,14 +155,14 @@ $out Read Operations Run on Secondary Replica Set Members
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 Starting in MongoDB 4.4, :pipeline:`$out` can run on 
-``replica set secondary nodes`` if all the nodes in
+replica set secondary nodes if all the nodes in
 cluster have :ref:`featureCompatibilityVersion <view-fcv>` set 
 to ``4.4`` or higher and the :doc:`/core/read-preference` is set to 
 secondary.
 
 Read operations of the :pipeline:`$out` statement occur on the 
-``secondary`` nodes, while the write operations occur only on the 
-``primary`` nodes.
+secondary nodes, while the write operations occur only on the 
+primary nodes.
 
 Not all driver versions support targeting of :pipeline:`$out` 
 operations to replica set secondary nodes. Check your 

source/release-notes/4.4.txt

@@ -394,7 +394,7 @@ Starting in MongoDB 4.4:
   output to a collection in the same database database where the 
   aggregation is run.
 
-- :pipeline:`$out` can only run on ``replica set secondary nodes`` if
+- :pipeline:`$out` can only run on replica set secondary nodes if
   all the nodes in cluster have 
   :ref:`featureCompatibilityVersion <view-fcv>` set to ``4.4`` or 
   higher and the :doc:`/core/read-preference` allows secondary reads.
@@ -434,7 +434,7 @@ Starting in MongoDB 4.4:
   only output to a collection in the same database where the aggregation 
   is run.
 
-- :pipeline:`$merge` can only run on ``replica set secondary nodes`` if
+- :pipeline:`$merge` can only run on replica set secondary nodes if
   all the nodes in cluster have 
   :ref:`featureCompatibilityVersion <view-fcv>` set to ``4.4`` or 
   higher and the :doc:`/core/read-preference` allows secondary reads.