First pass at replacing parent-child metaphor to describe docker links.

Addresses issue #7141

Docker-DCO-1.1-Signed-off-by: Fred Lifton <fred.lifton@docker.com> (github: fredlf)
"the", here, is redundant I believe.
It would work if the sentence was in the past tense, however, this format seemingly renders it so (i.e., redundant).