Update getting started doc to outline updating gemfile

GETTING_STARTED.md

@@ -1,6 +1,19 @@
 Getting Started
 ===============
 
+Update Your Gemfile
+-------------------
+
+If you're using Rails, you'll need to upgrade `factory_girl_rails` to the latest RC:
+
+    gem "factory_girl_rails", "~> 1.1.rc1"
+
+If you're *not* using Rails, you'll just have to change the required version of `factory_girl`:
+
+    gem "factory_girl", "~> 2.0.0.rc1"
+
+Once your Gemfile is updated, you'll want to update your bundle.
+
 Defining factories
 ------------------