For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:ojkastl_buildservice:WriteFreely/openSUSE_Tumbleweed/home:ojkastl_buildservice:WriteFreely.repo
zypper refresh
zypper install writefreely
For 16.0 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:ojkastl_buildservice:WriteFreely/16.0/home:ojkastl_buildservice:WriteFreely.repo
zypper refresh
zypper install writefreely
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:ojkastl_buildservice:WriteFreely/15.6/home:ojkastl_buildservice:WriteFreely.repo
zypper refresh
zypper install writefreely