Merge branch 'je/doc-push-upstream' into jch

Documentation updates.

* je/doc-push-upstream:
  SQUASH???
  doc: git-push: add explanation of `git push origin main`
  doc: git-push: clarify "what to push"
  doc: git-push: clarify "where to push"
  doc: add an UPSTREAM BRANCHES section to pull/push/fetch
  doc: git-push: clarify intro

diff --cc Documentation/git-push.adoc
Simple merge