Add README.md file for the docker directory

See issue #5873

Docker-DCO-1.1-Signed-off-by: Timothy <timothyhobbs@seznam.cz> (github: https://github.com/timthelion)
Add Dinesh Subhraveti to MAINTAINERS

Docker-DCO-1.1-Signed-off-by: Dinesh Subhraveti <dineshs@altiscale.com> (github: dineshs-altiscale)
Docs: add ApiVersion to /version for remote API 1.12

Docker-DCO-1.1-Signed-off-by: Paul Morie <pmorie@gmail.com> (github: pmorie)
Update contrib/check-config.sh to check for CGROUP_FREEZER (which is newly required), and to use /proc/mounts for checking if we have a cgroup hierarchy instead of using /proc/$$/mountinfo (which on systemd might not list the cgroup hierarchy)

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
utils: add test for TimeoutConn

Docker-DCO-1.1-Signed-off-by: Johan Euphrosine <proppy@google.com> (github: proppy)
registry: remove unneeded time.Duration()

These constants don't need to use time.Duration(). Fixup this file since
it seems to be the only one using this style.

Docker-DCO-1.1-Signed-off-by: Brandon Philips <brandon.philips@coreos.com> (github: philips)
Docs: Rename index with hub for ref. section

Docker-DCO-1.1-Signed-off-by: O.S. Tezer <ostezer@gmail.com> (github: ostezer)
Copy edits to Understanding Docker

Docker-DCO-1.1-Signed-off-by: Fred Lifton <fred.lifton@docker.com> (github: fredfl)
Merge pull request #6265 from fredlf/copyedits

Copyedits
Merge pull request #6295 from ostezer/docs-ref-index-hub

Docs: Rename index with hub for ref. section
Docker-DCO-1.1-Signed-off-by: Fred Lifton <fred.lifton@docker.com> (github: fredfl)
Docker-DCO-1.1-Signed-off-by: Fred Lifton <fred.lifton@docker.com> (github: fredfl)
Merge pull request #6298 from fredlf/copyedits

Edits to Win and OSX install
Fixed API 1.12 links and misc other fixes

Docker-DCO-1.1-Signed-off-by: James Turnbull <james@lovedthanlost.net> (github: jamtur01)
Updated Docker Hub documentation

Docker-DCO-1.1-Signed-off-by: James Turnbull <james@lovedthanlost.net> (github: jamtur01)
Merge pull request #6297 from jamtur01/hub

Updated Docker Hub documentation
Merge pull request #6299 from jamtur01/12link

Fixed API 1.12 links and misc other fixes
Update windows.md

Replace "OS X" by "Windows"
Merge pull request #6302 from Costent/patch-1

Update windows.md
Merge branch 'release' into merge_release_v1.0.0

Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)