Update README.md file

[Shuhua-L]

I suggest a few changes to the README file:

• Add a header section with links to the demo, issues, license, and more
• Add a Table of Contents
• Fix the link in the License section to point to the correct file

Here's a preview. If you approve, I'd like to create a PR

[ojasaklechayt]

I feel you can go for it