Fix typo. Add filenames above code.

[jDeppen]

No description provided.

[ryanflorence]

We changed the repo structure to make way more sense, previously the git history was part of the "structure" and that was a terrible idea, making PRs impossible to merge.

Now each lesson has its own directory so we can just click the merge button!

Mind updating your PR to work with the current code on the master branch? Thanks!