Copyedit notebooks to improve explanations and be more formal/less colloquial

[chmreid]

Notebooks as written are too colloquial, and should be more formal - "you/me/I" references and contractions should be removed, section titles hsould be clarified.

Clear, high-level explanations of what a notebook is demonstrating, who a notebook is for, or what is actually happening in the notebook are missing from some notebooks.

More clearly pointing readers to the HCA CLI and HCA API tutorials (see HumanCellAtlas/dcp-cli readthedocs page) would also be helpful.