Adds comments about MongoClient in the create manager file

Author: luislobo

lib/private/machines/create-manager.js

@@ -125,11 +125,15 @@ module.exports = {
     var mongoUrl = _clientConfig.url;
     _clientConfig = _.omit(_clientConfig, ['url', 'user', 'password', 'host', 'port', 'database']);
 
+    // Use unified topology. MongoDB node maintainers recommends this to be enabled
+    // https://github.com/mongodb/node-mongodb-native/releases/tag/v3.2.1
+    // Use new url parser to remove warnings
     _clientConfig = Object.assign({
       useNewUrlParser: true,
       useUnifiedTopology: true
     }, _clientConfig);
 
+    // http://mongodb.github.io/node-mongodb-native/3.5/api/MongoClient.html#.connect
     NodeMongoDBNativeLib.MongoClient.connect(mongoUrl, _clientConfig, function connectCb(err, client) {
       if (err) {
         return exits.error(err);