Brings the placeholder index.html more in line with WSK's basic.html

@addyosmani & @PaulKinlan, this updates the placeholder `index.html` to match what's found in https://github.com/google/web-starter-kit/blob/master/app/basic.html

If this looks to be what you had in mind, I'll update the individual samples to adopt the changes. 

Closes #4