Document what version of Docker is supported

docs/install.md

@@ -6,7 +6,7 @@ title: Installing Fig
 Installing Fig
 ==============
 
-First, install Docker. If you're on OS X, you can use [docker-osx](https://github.com/noplay/docker-osx):
+First, install Docker (version 0.8 or higher). If you're on OS X, you can use [docker-osx](https://github.com/noplay/docker-osx):
 
     $ curl https://raw.github.com/noplay/docker-osx/0.8.0/docker-osx > /usr/local/bin/docker-osx
     $ chmod +x /usr/local/bin/docker-osx