Update README.md

[eddyxu]

• [ ] Updates for new SQL syntax, i.e., model type
• [ ] Simplify README to be user facing features.
• [ ] Move developer facing content to project wiki

[da-liii]

I can publish rikai-ocr to pypi, and then, we can add docs like:

Rikai with community-maintained model types can be applied out of the box for:

• Object Detection [the link to demo notebook]()
• Optical Character Recognition [the link to demo notebook]
• (torchvision builtin models's application) ...