Update step_02.ngdoc

Request Type: docs

How to reproduce: None. Addition to make tutorial less confusing

Component(s): 

Impact: medium

Complexity: small

This issue is related to: 

**Detailed Description:**

Just a simple addition of text.

**Other Comments:**

Was going through the tutorial and got a little confused jumping from index.html to controllerSpec.js. Figured it out but could cause some confusion/frustration to some.