Add task for copying html templates in test to build

Fixes #88

## Problem
Consumers who have html templates in their test directory have to manually add a task to copy html templates in test to build.

## Solution
Add the task and entry in README

## Testing
- Add a `.html` file to the test dir
- Verify it gets copied to build/test after running `gulp test`

@evanweible-wf 
@trentgrover-wf