[doc request] Command Line needs document to guide users

[allencloud]

Issue Description
Currently we have implemented many cli commands in Pouch, While we have not finished the documentation work. Here I list the command line we have finished:

• pouch create
• pouch start
• pouch stop
• pouch version
• pouch info
• pouch volume create
• pouch volume rm
• pouch pull

I think document is as important as the code for this project. I suggest that finish this part as soon as possible.

/cc @alibaba/pouch

Describe what happened:
No command line document in project.

Describe what you expected to happen:
Command line doc exist in project.

How to reproduce it (as minimally and precisely as possible):
NONE

Anything else we need to know?:
NONE

Environment:

• pouch version (use pouch version):
• OS (e.g. from /etc/os-release):
• Kernel (e.g. uname -a):
• Install tools:
• Others: