Define ProbeFlow's JOSS scope and supported claims

[rohanplatts]

Purpose

• define exactly the features to be included for JOSS submission.
• define the scientific claims that require human validation.
• Identify gaps between the intended features and currently supported features (no more features, only less).
• Record this scope in repository documentation. We have largely discussed this during meetings, however we need to write it down, and document the current JOSS scope in the repository, (Scope.md ?), and edit this as expectations change in due course.

Completion criteria

• A written scope document exists in the repository.
• identified JOSS paper claim map to a feature that can realistically be
  independently validated.
• Experimental or unsupported features are clearly excluded or labelled.
• SPM-qt agree on proposed JOSS scope:
• Dr Peter Jacobson
• Gustavo Campi

Once the new branch is created, I will submit a PR of my drafted Scope.md, and Peter and Gustavo, you can request changes / approve in the comments, and I can revise the document to suit those requests.

separate implementation issues will be derived from scope.md.