Add navigation to the sample commands Jupyter Notebook

[yoda-vid]

Adds navigation links by using anchors tags. This navigation currently only works on viewers such as this: https://nbviewer.org/github/sanderslab/magellanmapper/blob/cleanup_notebook/bin/sample_cmds_bash.ipynb

In the GitHub viewer, the links apparently do not work because the page is shown within an iframe, and the links simply open the parent folder in the GitHub repo navigator.