add circle CI signal in README page

[yinghai]

Description

ATT. Make it easier to check the health of main trunk.

Fixes # (issue)

Type of change

Please delete options that are not relevant and/or add your own.

• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project (You can use the linters)
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas and hacks
• I have made corresponding changes to the documentation
• I have added tests to verify my fix or my feature
• New and existing unit tests pass locally with my changes
• I have added the relevant labels to my PR in so that relevant reviewers are notified