Create proper documentation of the app behavior (specification document)

[guilbep]

Create rfcs describing the app and architecture

[guilbep]

https://docs.google.com/document/d/1dHmKct_scrL32zT7FBkFmDMaXTfBUnz9/edit#heading=h.q9aqp6qvw14v

[guilbep]

need to create pull request @guilbep

[sphamba]

Documentation of newly developed features will be in backend/specs and will evolve through the whole lifetime of the project.
Todo:

• document current inner working