missing doc for 6896

Docker-DCO-1.1-Signed-off-by: Victor Vieux <vieux@docker.com> (github: vieux)
re-write to put the emphasis on the  format

Docker-DCO-1.1-Signed-off-by: SvenDowideit <SvenDowideit@home.org.au> (github: SvenDowideit)
Merge pull request #7045 from SvenDowideit/pr_out_re_write_to_put_the_emphasis_on_the_format

re-write to put the emphasis on the  format