On the Repositories page, sub section Third party repositories the EPEL example in the v7rc Docs still have the instructions for adding EPEL to Centos 6 :
Download and install release rpm from: http://dl.fedoraproject.org/pub/epel/6/x86_64/repoview/epel-release.html :
yum localinstall http://dl.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm -y
Should that be for 7 ? more like this :
yum localinstall http://dl.fedoraproject.org/pub/epel/7/x86_64/e/epel-release-7-8.noarch.rpm -y
EPEL is enabled by default on ns7.
We can remove that doc section completely or change the example, for RepoForge for instance.
RepoForge might be outdated. We have no updates since very long time.
It says on the site, and connecting to the packages seems to take forever, maybe RPM Fusion or Remi’s repo are interesting alternatives. Although RPM Fusion doesn’t seem to have EL7 packages, yet?.
But I think it would be good to keep the example.
Ps https://wiki.centos.org/AdditionalResources/Repositories/ also marks RepoForge as dead, do not use
Updated, thank you 
If you want to contribute to the manual, the whole source is on github