Make README point to other critical docker++ projects

People might find it hard to find the newer/related Docker projects,
especially when they're just github issues.  So, while I would have
preferred to have this at http://github.com/docker, I couldn't find
a doc to edit to make that happen, so this is the next best spot.

Signed-off-by: Doug Davis <dug@us.ibm.com>
Merge pull request #9565 from duglin/DocPtrs

Make README point to other critical docker projects