Request for centralization of man page and command line reference doc content

Description

As per the readme in the docker/docker.github.io repository command line help pages are generally generated via files in docker/cli. Unfortunately man/src and docs/reference/commandline share similar content. This means that either:

• The wrong file is modified to fix an issue with docker.github.io command line reference doc
• Both locations conflict with each other in content

My initial thought with this would be to have a templating like system with a centralized folder for both locations to pull shared content from. That said this has the potential to introduce additional template engine dependencies, the man build system, the docker.github.io deployment system, and any package release systems.

Steps to reproduce the issue:

1. Notice an issue with one of the reference command doc pages in docker/docker.github.io
2. Find the file it matches in the repo
3. The file says that the content is auto-generated from docker/cli and to search for the content in that repository
4. Locate the content in the repository
5. Change the file

Describe the results you received:

I changed the file located in man/src that has the content, only to find out I needed to change it in docs/reference/commandline instead.

Describe the results you expected:

Change it in a single location.

Output of docker version:

Client:
 Version:      18.03.1-ce
 API version:  1.37
 Go version:   go1.9.5
 Git commit:   9ee9f40
 Built:        Thu Apr 26 07:13:02 2018
 OS/Arch:      darwin/amd64
 Experimental: false
 Orchestrator: swarm

Output of docker info:

Server:
 Engine:
  Version:      18.03.1-ce
  API version:  1.37 (minimum version 1.12)
  Go version:   go1.9.5
  Git commit:   9ee9f40
  Built:        Thu Apr 26 07:22:38 2018
  OS/Arch:      linux/amd64
  Experimental: true
MSW3FCG8WL:~ chri0786$ docker info
Containers: 5
 Running: 0
 Paused: 0
 Stopped: 5
Images: 20
Server Version: 18.03.1-ce
Storage Driver: overlay2
 Backing Filesystem: extfs
 Supports d_type: true
 Native Overlay Diff: true
Logging Driver: json-file
Cgroup Driver: cgroupfs
Plugins:
 Volume: local
 Network: bridge host ipvlan macvlan null overlay
 Log: awslogs fluentd gcplogs gelf journald json-file logentries splunk syslog
Swarm: inactive
Runtimes: runc
Default Runtime: runc
Init Binary: docker-init
containerd version: 773c489c9c1b21a6d78b5c538cd395416ec50f88
runc version: 4fc53a81fb7c994640722ac585fa9ca548971871
init version: 949e6fa
Security Options:
 seccomp
  Profile: default
Kernel Version: 4.9.87-linuxkit-aufs
Operating System: Docker for Mac
OSType: linux
Architecture: x86_64
CPUs: 4
Total Memory: 1.952GiB
Name: linuxkit-025000000001
ID: WXX3:3LTB:U6JB:IG33:VZZR:P5RL:DPVC:ZOTZ:37FB:XRYC:AKZK:5HWP
Docker Root Dir: /var/lib/docker
Debug Mode (client): false
Debug Mode (server): true
 File Descriptors: 21
 Goroutines: 40
 System Time: 2018-07-08T12:15:26.3107717Z
 EventsListeners: 2
HTTP Proxy: docker.for.mac.http.internal:3128
HTTPS Proxy: docker.for.mac.http.internal:3129
Registry: https://index.docker.io/v1/
Labels:
Experimental: true
Insecure Registries:
 127.0.0.0/8
Live Restore Enabled: false

Start with the README in engine/reference/commandline, then compare the duplicated content in man/src and docs/reference/commandline. Determine how both locations can use one source without disrupting the man build or docker.github.io deployment. Done means command-line reference content is maintained in a single location and both outputs remain consistent.