Update Guide.md

    subscriptions:  {
      this.subscribe('items');
    
      // add the subscription to the waitlist
      this.subscribe('item', this.params._id).wait();
    },

Should be 

    subscriptions: function() {
      this.subscribe('items');
    
      // add the subscription to the waitlist
      this.subscribe('item', this.params._id).wait();
    },