DOCS-872 rewrite comments about nearest and tag sets and member selection

Author: Ed Costello

source/applications/replication.txt

@@ -284,8 +284,8 @@ behavior <replica-set-read-preference-behavior>`. See also the
    on read operations without preference for current or stale data.
 
    If you specify a :ref:`tag set <replica-set-read-preference-tag-sets>`,
-   the client attempts to find a secondary member that matches the
-   specified tag set and directs reads to a random secondary from
+   the client attempts to find a replica set member that matches the
+   specified tag set and directs reads to an arbitrary member from
    among the :ref:`nearest group <replica-set-read-preference-behavior-nearest>`.
 
    Read operations using the :readmode:`nearest` mode may return stale data.