Merge branch 'mg/reset-doc'

* mg/reset-doc:
  git-reset.txt: make modes description more consistent
  git-reset.txt: point to git-checkout
  git-reset.txt: use "working tree" consistently
  git-reset.txt: reset --soft is not a no-op
  git-reset.txt: reset does not change files in target
  git-reset.txt: clarify branch vs. branch head