It feels that the details of decisions for proposals are a bit hidden, we sometimes put them in the commit message. See https://github.com/alphagov/govuk-design-system-architecture/commit/10e4eb3c192d398a893aab61d20e65e4ccf8dd37 and https://github.com/alphagov/govuk-design-system-architecture/pull/12/commits/36f14f90bd34486d64cd9b27d9d90f539cca6f09 We should move them into the doc themselves.
