docs(README.md) improve documentation
docs(README.md) improve documentation

- Improve readability of the project documentation.
- Add missing Markdown syntax to make things easier to read.
- Fix broken URL path to index.html

More details about Markdown syntax:
- https://guides.github.com/features/mastering-markdown/
- https://github.com/adam-p/markdown-here/wiki/Markdown-Cheatsheet
- https://ia.net/writer/support/general/markdown-guide/
- https://en.support.wordpress.com/markdown-quick-reference/

OAButton/website,OAButton/oab_static,OAButton/oab_static,OAButton/website