add mongodb connect db

Author: boiawang

models/user.js

@@ -11,4 +11,6 @@ var UserSchema = new Schema({
     sex: Number
 });
 
-exports.User = mongoose.model('User', UserSchema);
+exports.User = mongoose.model('User', UserSchema);
+
+mongoose.connect('mongodb://127.0.0.1:27017/chat_user');