Merge branch 'nk/ref-doc' into maint

* 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

diff --cc Documentation/git.txt
Simple merge

diff --cc Documentation/glossary-content.txt
Simple merge