Some additions to the suggested Atom set up

Hi Abigail,
I've just started to use Atom and managed to automatically associate the correct grammar/syntax highlight to both js and html file.
This requires installing another couple of packages plus some more tricky configuration.

Hopefully this might be useful to other developers finding themselves follow your suggestions to get a good Atom set up (like I did!).

Thank you very much for the great package,
feel free to ignore this PR if you're not comfortable with it.

Luca