Adds notebook for Jaccard Similarity (#71)

This PR adds a notebook to demonstrate nx-cugraph's support for `nx.jaccard_coefficients()` by implementing a simple movie recommendation system based on MovieLens data.

This notebook will also be made available in Google Colab and referenced in an upcoming blog.

Authors:
  - Rick Ratzel (https://github.com/rlratzel)
  - Ralph Liu (https://github.com/nv-rliu)

Approvers:
  - Ralph Liu (https://github.com/nv-rliu)
  - Erik Welch (https://github.com/eriknw)

URL: #71