Writing style guide / glossary for Jupyter

[JasonWeill]

Some terms in Jupyter projects, such as console and main work area, may not be familiar to less experienced users. We have a TypeScript style guide for code contributors, but not a writing style guide or glossary that defines the various parts of our application's UI and data model. Add a style guide or glossary to the documentation, wiki, or other persistent location. Include annotated diagrams, such as a screenshot of the Lab UI with callouts to individual elements.

It's fine to defer to an existing style guide, like the Fedora Documentation Style Guide or the Microsoft Writing Style Guide, for topics not specifically covered by the Jupyter writing style guide.