Add description to gem

Rakefile

@@ -11,7 +11,12 @@ begin
     s.email     = "bryan" + "@" + "brynary.com"
     s.homepage  = "http://github.com/brynary/rack-test"
     s.summary   = "Simple testing API built on Rack"
-    # s.description = "TODO"
+    s.description  = <<-EOS.strip
+Rack::Test is a small, simple testing API for Rack apps. It can be used on its
+own or as a reusable starting point for Web frameworks and testing libraries
+to build on. Most of its initial functionality is an extraction of Merb 1.0's
+request helpers feature.
+    EOS
     s.rubyforge_project = "rack-test"
     s.extra_rdoc_files = %w[README.rdoc MIT-LICENSE.txt]
   end