There is an arduino package on community-testing though I installed arduino-git from AUR. I did the installation in fresh Archlinux on Raspberry Pi 3, and that took me more than an hour. Furthermore, beware that the arduino-git package is more than 4GB.
The basic instructions to setup the arduino uno wifi are here. When you connect the arduino board via USB to your computer you can access the device via wifi connection. This network is not protected. Follow the aforementioned instructions and change the arduino's mode to STA. This will make your board only visible to your local network.
Then you have to follow the steps 1 & 2 from here and make sure you don't have modemmanager installed (see Step 3). Finally open the IDE and select the correct port and board.
$ sudo vim /etc/udev/rules.d/90-extraacl.rules
Paste the following content:
KERNEL="ttyUSB[0-9]*", TAG+="udev-acl", TAG+="uaccess", OWNER="<your_username>" KERNEL="ttyACM[0-9]*", TAG+="udev-acl", TAG+="uaccess", OWNER="<your_username>"
Change group permissions:
$ sudo usermod -a -G tty <your_username> $ sudo usermod -a -G uucp <your_username>