Update React & Webpack.md

[cseas]

Added a note to clarify the use of externals property in webpack config.

I followed this guide as my first webpack tutorial then moved on to webpack docs to learn more and add more things to the webpack config. None of the other tutorials I saw had manually added any React libraries to index.html so I removed those 2 lines and struggled for about a week to realize the externals field added from this tutorial was the reason my site stopped working.

I personally wouldn't recommend adding any externals to a beginner tutorial. Learning webpack is complex enough as it is. Something like externals should only be introduced in a "Production/Deployment" or "Optimizations" related page after a beginner has gone through the initial tutorial without hiccups. But if that has to be included in this beginner tutorial, the purpose of it should be made really clear.

[orta]

Thanks, this page has been replaced with a redirect to the official webpack docs for TypeScript - so people shouldn't get caught up in it in the future