Provide instruction on installing build essentials for gems with C extensions

Closes #59

Author: nilbus

README.md

@@ -56,6 +56,10 @@ Initial Setup
 
 1. [Install drivers for the USB serial connector](https://github.com/nilbus/pinewood-derby/wiki/USB-serial-driver-installation)
 1. Install [Ruby >= 2.0.0](https://www.ruby-lang.org/en/downloads), [bundler](http://bundler.io), and [node.js][http://nodejs.org].
+1. Install build tools for your operating system:
+  a. **Mac OSX**: Install the _Xcode command line tools_
+  b. **Ubuntu/Debian Linux**: `sudo apt-get install build-essential`
+  c. **Fedora/CentOS/RedHat Linux**: `yum groupinstall "Development Tools"`
 1. Install the required ruby dependencies
 
         bundle install