Clarify docs for @hot-loader/react-dom
Clarify docs for @hot-loader/react-dom

By using the name of the package `@hot-loader/react-dom` instead of
"React-🔥-Dom" right away we're making it more obvious and accessible
what we're talking about; people will be able to instantly search for
that package instead of wondering what it is and where it's explained.

gaearon/react-hot-loader,gaearon/react-hot-loader