[Documentation] Could we add more documentations & use cases for React.PureComponent

[tjcchen]

Hello React Dev Team:

After searching a lot of chapters concerning React.PureComponent, I still found the information provided is not sufficient for a developer to start using PureComponent in their project.

Could we adding more intros to this part? Thanks in advance!

Doc: https://reactjs.org/docs/react-api.html#reactpurecomponent

Thanks,