The structure of the document that records longer-term project
decisions to deprecate/remove/update various behaviour has been
outlined.
* ps/document-breaking-changes:
BreakingChanges: document that we do not plan to deprecate git-checkout
BreakingChanges: document removal of grafting
BreakingChanges: document upcoming change from "sha1" to "sha256"
docs: introduce document to announce breaking changes