Add GitHub account Prerequisite for K8s contribution

As a brand new contributor, I didn't realise I needed a GitHub account. I want to make sure it's clear for others.

Author: jaytiaki

contributors/guide/README.md

@@ -15,6 +15,7 @@ description:
   - [Welcome](#welcome)
   - [Contributor Guide](#contributor-guide)
   - [Prerequisites](#prerequisites)
+    - [Create a GitHub account](#create-a-github-account)
     - [Sign the CLA](#sign-the-cla)
     - [Code of Conduct](#code-of-conduct)
     - [Setting up your development environment](#setting-up-your-development-environment)
@@ -60,6 +61,10 @@ prerequisites. These steps are checked automatically by [a bot] during your
 first submission.  Completing these steps will make your first contribution
 easier: 
 
+### Create a GitHub account
+
+Before you get started, you will need to [signup](http://github.com/signup) for a GitHub user account. 
+
 ### Sign the CLA
 
 Before you can contribute to Kubernetes, you will need to sign the