Add license scan report and status

[fossabot]

Your FOSSA integration was successful! Attached in this PR is a badge and license report to track scan status in your README.

Below are docs for integrating FOSSA license checks into your CI:

• CircleCI
• TravisCI
• Jenkins
• Other

[lucab]

I'm not sure where this is coming from but I think somebody manually pointed it at this repo; if so, can you please comment back here?

[breezewish]

@lucab I think this is related to some recent attempts to add FOSSA to TiKV org repos.

@zhouqiang-cl Do we need this badge here?

[zhouqiang-cl]

@lucab I think this is related to some recent attempts to add FOSSA to TiKV org repos.

@zhouqiang-cl Do we need this badge here?

I am process the fossa check. Please let the PR hang here for few days.