Two Hints today 😉
Ok, to add/activate the AUR-Repository in the Manjaro-Linux Software-Center, go to Settings like in the Screenshot:
Then click on Settings („Einstellungen“ in german 😉 ) It will open the following window:
Then activate the AUR-Repository. Thats it!
If you want to install something from AUR, simple click on the search-field and start typing.
Have fun 🙂