DOCS-11964: distinct and snapshot rc

Author: kay-kim

source/reference/read-concern.txt

@@ -271,15 +271,15 @@ The following operations support read concern:
      - |checkmark|
      - |checkmark|
      - |checkmark|
-     - |checkmark|
+     - 
      - |checkmark|
 
    * - :dbcommand:`distinct`
 
      - |checkmark|
      - |checkmark|
      - |checkmark|
-     - |checkmark|
+     - |checkmark| [#distinct]_
      - |checkmark|
 
 
@@ -335,6 +335,12 @@ The following operations support read concern:
 
    .. include:: /includes/extracts/4.2-changes-out-linearizable.rst
 
+.. [#distinct]
+
+   Read concern :readconcern:`"snapshot"` is available only for
+   multi-document transactions. In a transaction, you cannot use the
+   ``distinct`` command or its helpers on a sharded collection.
+   
 The following write operations can also accept a read concern if part
 of a multi-document transaction: