Merge branch 'nk/ref-doc'

Merge branch 'nk/ref-doc'

* nk/ref-doc:
  glossary: clarify description of HEAD
  glossary: update description of head and ref
  glossary: update description of "tag"
  git.txt: de-emphasize the implementation detail of a ref
  check-ref-format doc: de-emphasize the implementation detail of a ref
  git-remote.txt: avoid sounding as if loose refs are the only ones in the world
  git-remote.txt: fix wrong remote refspec