Add testing docs install instructions

[davelab6]

Something like:

---

For testing v0.109 (development release) on Fedora 23, Fedora 24 or Fedora Rawhide, we have a COPR repository that you can install very quickly:

https://copr.fedorainfracloud.org/coprs/samtoday/sugar

If you already have Sugar installed on F23+, to upgrade your sugar to .you can just run the following commands:

dnf copr enable samtoday/sugar;
dnf update;

To try out the cutting edge developer's versions, check out the developer documentation

[quozl]

no longer maintained.