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