404 hyperlink in README

Created by: evalexpr

At the bottom of README.md there's a hyperlink to some docs which previously would take you to https://reactjs.org/docs/package-management.html

This html page seems to no longer exist, I guess it used to be equivalent to the page I've found here: https://zhenyong.github.io/react/docs/package-management.html

Can't seem to find a comparable entry in the new docs which contains the information that package-management used to contain. Just an entry on optimizing browserify & webpack (https://reactjs.org/docs/optimizing-performance.html#browserify)

If someone wants to suggest the correct page this hyperlink should forward to then I'd be happy to make a PR