Tweak docs

[past-due]

To clarify expectations, and ensure that there's a shared understanding going forwards, we're adding some language surrounding rollbacks, submitter responsibilities, and more to the document to ensure that people are aware and on the same page.

On rollbacks:

We want to allow for the potential slight reduction in threshold for what are considered partial or full rollbacks of recent changes, as there’s an expectation that opinions might be revised as a result of actually experiencing a merged change in a recent release.

As much as we are grateful for all of the testing that people do when initially reviewing these proposals, we do expect that opinions might change once everyone is playing with a change fulltime. A slight reduction in threshold for rollbacks allows that, and we hope it'll help contribute to the balance maintaining a happy setpoint going forwards.