README.md: Refactor the README.md (#3009)
README.md: Refactor the README.md (#3009)

* README.md: Refactor the README.md

* README.md: Talk about dev target and check more

* README.md: Correct dependency reasons

* README.md: Correct spelling & use better link.

BusyJay/tikv,BusyJay/tikv,pingcap/tikv,BusyJay/tikv,BusyJay/tikv,c4pt0r/tikv,pingcap/tikv