updated README

README

@@ -39,3 +39,16 @@ _A simple and flexible static site generator_
   emails. This works well if you host projects on GitHub, which is already very
   markdown friendly. You can run a Petrify site generator on the doc directory
   of your project and have pretty HTML docs for your own domain.
+
+## Getting started
+
+First, install the latest version of [node.js](http://nodejs.org/#download).
+Petrify uses git submodules for the rest of its dependencies. Once you've
+cloned the repository, do:
+
+    git submodule update --init --recursive
+
+Then, cd to the examples directory and run the build script. This will create
+a www directory with a bunch of HTML files inside. Voila! you've just generated
+your first site. For now, the example site and the files in the doc directory
+will have to be enough to get you started.