One-line the gem install commands

README.md

@@ -4,9 +4,7 @@ Polymer docs are mostly in Markdown with some HTML. [Jekyll][jekyll] is used to
 
 We use Jekyll 1.4.2+ and [Grunt][grunt] to generate the documentation. You'll need to install the requirements before working on the docs (these instructions assume [NPM is already installed](http://nodejs.org/download/)):
 
-    gem install jekyll
-    gem install kramdown
-    gem install jekyll-page-hooks
+    gem install jekyll kramdown jekyll-page-hooks
     npm install -g grunt-cli
 
 **Note:** If you receive permission warnings, you may need to run the above tasks with `sudo`.