[Feat][Doc] Update the repository url and the docs url

[acezen]

Proposed changes

related #432 changes include:

• repo location update: aliabab/GraphAr -> apache/incubator-graphar
• websize update: alibaba.github.io/GraphAr -> graphar.apache.org
• README.rst -> README.md

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• [x] I have read the CONTRIBUTING doc
• [x] I have signed the CLA
• [ ] Lint and unit tests pass locally with my changes
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have added necessary documentation (if appropriate)