Update `template.hbs`

* Fix `Hello World Guide` link.
* Use `https` where possible.
* Specify the language of the HTML document
  (for more information on why that is important, see:
   https://github.com/h5bp/html5-boilerplate/issues/1542).

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@jlord at first I've tried to [correct this](https://github.com/jlord/patchwork/pull/626) in the wrong repository.