DOCSP-48717 Update non-MongoDB Credentials

Author: lindseymoore

source/quick-start/create-a-connection-string.txt

@@ -51,7 +51,7 @@ To connect to an instance or deployment not hosted on Atlas, see
    .. step:: Update the Placeholders
 
       Paste this connection string into a a file in your preferred text editor
-      and replace the "<username>" and "<password>" placeholders with
+      and replace the "<db_username>" and "<db_password>" placeholders with
       your database user's username and password.
 
       Save this file to a safe location for use in the next step.