Merge branch 'kh/update-ref'

Documentation updates to 'git-update-ref(1)'. * kh/update-ref: Documentation: mutually link update-ref and symbolic-ref Documentation/git-update-ref.txt: discuss symbolic refs Documentation/git-update-ref.txt: remove confusing paragraph Documentation/git-update-ref.txt: demote symlink to last section Documentation/git-update-ref.txt: remove safety paragraphs Documentation/git-update-ref.txt: drop “flag”