From my BUGS page for the Asus X205TA.

The touchpad should work on kernels 4.3* [1] (confirmed on kernel 4.3.3-2-ARCH), but if you still run into problems on another kernel, you can proceed with the following.

First, make sure that you have xf86-input-synaptics installed. To enable more features of the touchpad:

Then,

# nano /etc/X11/xorg.conf.d/elan_synaptics.conf
---------------------------------------------------
Section "InpuClass"
`