Update dockerlinks.md for consistency

The parent/child metaphor should be consistent. If db is the parent (after all, it was created first), then the child is accessing information of the parent, not the other way around. I believe these edits make the text more clear/readable.
We need to be consistent in our use of this term. Either hyphen or slash work for me (parent-child or parent/child). We just need to pick one and use it consistently throughout.