Linking notebooks into index

[tracykteal]

I have a PR in to update this repo with the Carpentries template.
#30

I moved all the original files into the 'notebooks' directory.

We'll link to the notebooks for each lesson in the index.html file. We need to add those links on the index page, and also make sure that things still work with the notebooks with the files moved around.

[kellieotto]

@tracykteal I updated the index page. Does this look right?