Create documentation

[doodspav]

At minmum:

• for users:
  • introduction (uses cases and such)
  • core design decisions and goals
  • version guarantees
  • how to build/install
  • changelog
  • documentation for all APIs (as well as their guarantees)
  • examples on how to use them
  • API reference list (should this be separate?)
  • FAQ
• for contributors:
  • rules (like code style, branch convention, etc...)
  • architecture diagram
  • example of how to support a new architecture or implementation
• other
  • test results?
  • code coverage?

Also:

• basic readme
• badges showing coverage and pipeline info