Added docs for installing from master.

site/docs/installation.md

@@ -71,6 +71,18 @@ use the `-v` switch to indicate the version you'd like to install:
 gem install jekyll -v '2.0.0.alpha.1'
 {% endhighlight %}
 
+If you'd like to install a development version of Jekyll, the process is a bit
+more involved. This gives you the advantage of having the latest and greatest,
+but may be unstable.
+
+{% highlight bash %}
+$ git clone git://github.com/jekyll/jekyll.git
+$ cd jekyll
+$ script/bootstrap
+$ bundle exec rake build
+$ ls pkg/*.gem | head -n 1 | xargs gem install -l
+{% endhighlight %}
+
 ## Optional Extras
 
 There are a number of (optional) extra features that Jekyll supports that you