Create help page for SlicerQREADS

Suggested approach:
* [ ] 1. Create help in a google document
* [ ] 2. Once this is complete, we will revisit how to publish the content (using a simple GitHub page or readthedocs or ...)

No files, tests, or documentation entry points are named. Start by defining the help content in a Google document, then revisit whether to publish it through a GitHub page or Read the Docs; the work is done when the help content and a publication approach are agreed.

Written by the indexing model from the issue text.