Update flag usages and docs for max restart count

Signed-off-by: Michael Crosby <michael@docker.com>
Add link to Ubuntu notes about LTSEnablementStack

When running Ubuntu with a graphical environment, the kernel version MUST match the Xorg version. Only installing the suggested packages above breaks Unity for anything other than 2D mode (in VMware and probably native).
Signed-off-by: Ethan Spoelstra <ewspoelstra@computerphreaks.com>
Added manual installation instruction for Centos7.
Added a note about firewalld.

Signed-off-by: Nicolas Goy <kuon@goyman.com>
Merge pull request #7574 from crosbymichael/update-restart-docs

Update flag usages and docs for max restart count
Merge pull request #7603 from kuon/centos7

Added manual installation instruction for Centos7 and note about firewalld.
small word change

Docker-DCO-1.1-Signed-off-by: SvenDowideit <SvenDowideit@home.org.au> (github: SvenDowideit)
Merge pull request #7732 from SvenDowideit/ubuntu-backported-kernel

Ubuntu backported kernel