By default, docker containers inherit ulimit from limits of docker
deamon. On CentOS 7, docker daemon default NOFILE is 1048576.
It can found in /usr/lib/systemd/system/docker.service.
The big limit will cause many problem. we should control it in
production environment.

Change-Id: Iab962446a94ef092977728259d9818b86cfa7f68

Change index to ease identify what service want to look.
Split docs into more specific folder such as networking
and storage.

Change-Id: Ic7ac12b3dd555fa5c018eeb897ccd4a5a2dfe8f3