Update index.html

Some small changes I did while reviewing the code:

* Trim trailing whitespace.
* Lowercased the doctype. No reason for it to be inconsistent with the other html tags.
* Replace the 'old' way of declaring the charset with the html5 way.
* Language indicator added.
* Since we don't want our sites to render with a IE7 engine, let's include the `IE=edge` meta info.