DOCSP-42303: Update username/password placeholders (#987)

Author: mcmorisi

source/swift.txt

@@ -66,7 +66,7 @@ Connect to MongoDB Atlas
          }
 
          // replace the following string with your connection uri
-         let uri = "mongodb+srv://<username>:<password>@<cluster-address>/test?w=majority"
+         let uri = "mongodb+srv://<db_username>:<db_password>@<cluster-address>/test?w=majority"
          let client = try MongoClient(uri)
 
          // print a list of database names
@@ -85,7 +85,7 @@ Connect to MongoDB Atlas
          let elg = MultiThreadedEventLoopGroup(numberOfThreads: 4)
 
          // replace the following string with your connection uri
-         let uri = "mongodb+srv://<username>:<password>@<cluster-address>/test?w=majority"
+         let uri = "mongodb+srv://<db_username>:<db_password>@<cluster-address>/test?w=majority"
 
          let client = try MongoClient(
              uri,