Prepare notebooks for Rocky

[tschaffter]

As a user of the NLP Sandbox, I want to see user-friendly notebooks to perform the most common tasks so that I can focus on developing tools or applying them.

• Develop a notebook to illustrate all the data node operations #9
• Develop a notebook to evaluate the performance of a PHI annotator #21
• Develop a notebook to compare the content of multiple datasets #22
• Add Jupyter to this repository #23