Change instructions to download archive

Before, we instructed participants to clone the git repo. This is easy, except when it isn't. If the user does not have git-lfs installed, which is relatively likely, then the data files (particularly kitchen.vtk) will not be included. This is a problem as it means running the tutorial examples will fail.

Instead, go back to instructing users to download a tarball. Rather than point them to a release, include the files with the proper edits here.