You can install it on your own server if you are on their $200/m plan. Otherwise a datacenter can partner with them by setting up a dedicated server to run the daemon for everyone in the datacenter. Even if they are on cloudflare's free plan you can take advantage of railgun if you are at a partnered data center.
That looks interesting, I didn't know they had that. Looks like a simple daemon you install on your own server. Nice!
Any chance OVH could become a CloudFlare Railgun partner?
https://www.cloudflare.com/railgun
Seems like only one railgun server is needed per OVH datacenter.
Should help speed up OVH sites in locations like Australia where OVH don't have any peering.