DOCSP-20161 fix confused shell reference v5.2 (#174)

* DOCSP-20161 Fix confused shell reference

* Clarify shells

* Missing comma

* Review feedback

* Wording tweak

Author: Dave

source/reference/method/db.getMongo.txt

@@ -22,7 +22,8 @@ db.getMongo()
 
 .. note::
 
-   :binary:`~bin.mongosh` has a sub-command,
-   ``db.getMongo().setSecondaryOk()`` which is not available in
-   ``mongosh``. Use :method:`Mongo.setReadPref()` instead.
+   The legacy :binary:`mongo` shell has a sub-command,
+   ``db.getMongo().setSecondaryOk()``, which is not available in
+   :binary:`mongosh`. In :binary:`mongosh`, use
+   :method:`Mongo.setReadPref()` instead.