gtk-doc from GNOME:STABLE:3.16 project
Select Your Operating System
Add repository and install manually
For openSUSE 13.2 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/GNOME:STABLE:3.16/openSUSE_13.2/GNOME:STABLE:3.16.repo zypper refresh zypper install gtk-doc