Clean up + add documentation

[isabelizimm]

In order to create a better end-to-end demo experience, I would like to update this repo in the following ways:

• [X] Update README.md to include DevConf.CZ info, project overview, and contact info
• [X] Refactor notebook (remove test-set image for personal photo, update explainer)
• [X] Add explainer for image detection failure
• [X] Add prose to notebook to enhance user experience