Some improvements have been made. Now xfce4-notifyd has been installed as a dependency for manjaro-lxde-settings in order to get notifications. Also, after manjaro-lxde-settings version 20170427 hits your repositories (it's currently on unstable branch) you will also get a GUI tool for managing the notifications as well as the i3-scrot package. No manual intervention is needed, these will get installed automatically.
The only manual change you might wanna do (it's not necessary) is changing the scrot command to i3-scrot command for Print shortcut at "Setup Hot Keys" application (of course after manjaro-lxde-settings-20170427 reaches your repository and gets installed). If you do that, then you will get a notification after you take a screenshot