Add the demo link to Readme

[guangxuli]

** Question?(Go ahead, ignore issue template) **
no

Bug or Feature?:
no, just enhance

Expected Behavior:
Access the link correctly.

Current Behavior:
There is no demo link in Readme.

How to reproduce(The more detailed the better):
just check the readme~

Your Environment:

• Kubernetes version:
• Hardware or VM configuration:
• OS (e.g. from /etc/os-release):
• Kernel (e.g. uname -a):

[guangxuli]

/assign