Update contributing guide for Windows dev

Please read over Windows section for prereqs.

CONTRIBUTING.md

@@ -15,17 +15,20 @@ Before you fil an issue or a pull request, quickly read of the following tips on
  - [Testing](#testing)
  - [License](#license)
 
-### Prerequisites
 
+### Prerequisites for developing Kitematic on Mac 
+You will need to install: 
 -  [Node.js 0.10.38](https://nodejs.org/dist/v0.10.38/)
-
-### Other Prerequisites (Mac)
 - The latest Xcode from the Apple App Store. 
 
-### Other Prerequisites (Windows)
-- [Visual Studio 2013 Community](https://www.visualstudio.com/en-us/products/visual-studio-community-vs.aspx) (or similar) - Kitematic does not need any optional packages. 
+### Prerequisites for developing Kitematic on on Windows 
+You will need to install: 
+- [Node.js 0.10.38](https://nodejs.org/dist/v0.10.38/)
+- Open a command prompt (`cmd`) and run the command `mkdir ~/AppData/Roaming/npm` 
+- [Visual Studio 2013 Community](https://www.visualstudio.com/en-us/products/visual-studio-community-vs.aspx) (or similar) - You do not need to install any optional packages during install.
 - [Python](https://www.python.org/downloads/release/python-2710/)
 
+
 ### Getting Started
 
 - `npm install`
@@ -34,7 +37,7 @@ To run the app in development:
 
 - `npm start`
 
-Running `npm start` will download and install the OS X Docker client,
+Running `npm start` will download and install the Docker client,
 [Docker Machine](https://github.com/docker/machine), [Docker Compose](https://github.com/docker/compose)
 the [Boot2Docker iso](https://github.com/boot2docker/boot2docker),
 [Electron](http://electron.atom.io/).