Add details about when to dismiss stale PR reviews
Add details about when to dismiss stale PR reviews

This commit adds a new rule about dismissing stale PR reviews when making changes before merging, unless they are minor changes and the author is confident there are no side-effects.

It also adds two example of the new rule at work.
alphagov/govuk-developer-docs,alphagov/govuk-developer-docs,alphagov/govuk-developer-docs,alphagov/govuk-developer-docs