File: engine/installation/linux/fedora.md

The section on creating a dnf|yum repo for docker on fedora 25 does not work, because there is not a 25/ folder at this url currently.

https://yum.dockerproject.org/repo/main/fedora/

Fix by adding the folder and the appropriate contents or by mentioning that support for Fedora 25 isn't available yet.