Make the `master` branch to be protected after we got one more commiters

[huan]

So that we can improve the code quality for our master branch.

To be done.

[jcai]

禁止force push?

[huan]

Yes. after the branch has been protected, the force push will be forbidden.

And there are also other benefits:

1. need to use Pull Request to merge code into the master branch
2. The CI must turn green
3. Requires code review & approval