Add some kind of an "Assisted do-ocracy pledge" toward contributions (from within and outside the team)

I am thinking around these lines

- This is a collaborative project and contributions to any component from any developer and outside contributor(s) are welcome
- DANDI project encourages submitting PRs to resolve outstanding issues, in particular with severity-important and severity-critical labels
- The primary developer team of the corresponding component pledges to provide timely feedback to bring submitted PRs to the acceptable state (and resort to provide an alternative implementation only if significant changes are required)

WDYT @dandi/dandiarchive @dandi/archive-maintainers @dandi/dandi-cli (we need to come up with `@dandi/people` super-team... will do some time)