Add proposal for ADR

This is just an idea, based on the posts:

https://cognitect.com/blog/2011/11/15/documenting-architecture-decisions https://understandlegacycode.com/blog/earn-maintainers-esteem-with-adrs/

The main idea is to document any architectural decisions taken over time, and at any point being able to reason about past decisions to understand the current state of the system.

You can for instance manage the ADRs with this program: https://github.com/npryce/adr-tools

Edit: another interesting post about ADRs: http://beza1e1.tuxen.de/decision_records.html