update credentials

Author: shuangela

source/connect/connection-targets.txt

@@ -30,8 +30,8 @@ To connect to a MongoDB deployment on Atlas, include the following elements
 in your connection string:
 
 - The URL of your Atlas cluster
-- Your MongoDB username
-- Your MongoDB password
+- Your MongoDB database username
+- Your MongoDB database password
 
 Then, pass your connection string to the ``MongoClient`` constructor.
 

source/connect/mongoclient.txt

@@ -52,10 +52,10 @@ A standard connection string includes the following components:
      - Required. A prefix that identifies this as a string in the
        standard connection format.
 
-   * - ``username:password``
+   * - ``db_username:db_password``
 
      - Optional. Authentication credentials. If you include these, the client
-       authenticates the user against the database specified in ``authSource``.
+       authenticates the database user against the database specified in ``authSource``.
        For more information about the ``authSource`` connection option, 
        see :ref:`kotlin-sync-auth`. 
 
@@ -67,7 +67,7 @@ A standard connection string includes the following components:
    * - ``/defaultauthdb``
 
      - Optional. The authentication database to use if the
-       connection string includes ``username:password@``
+       connection string includes ``db_username:db_password@``
        authentication credentials but not the ``authSource`` option. If you don't include 
        this component, the client authenticates the user against the ``admin`` database.