Restructure architecture design document collection (ADR = Architecture Decision Records)

[ERnsTL]

Currently, architecture resp. design documents exist in an unstructured way in doc/.

Goals for design documents:

• be numbered
• be current
• conform to a common structure
• live in doc/ or a subdirectory thereof.

Observation:

• There must be an over-arching strategy document for project direction and positioning of flowd = flowd manifesto.