Update documentation, add file compression

[dbertella]

As proposed in #1908 and #3169 gzip file can be just a postbuild script in the package.json, here is a simple example in the README.md file

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[Timer]

Thanks for this PR! What's the story for Windows compatibility? Is there an npm package we can use instead?

[gaearon]

Typically web server takes care of this. Do we really need it?

[Timer]

Probably not.

[gaearon]

I'd say let's leave it to web servers.

[yairEO]

While web servers do this, I would like to say that I currently am working on a simple dashboard for a client, and the client demanded the code to be serve statically (via S3 bucket).

After I've tried my best to convince the client to at least set up a simple server, the client agreed and is using serve

This simply "server" apparently doesn't know how to gzip on-the-fly.
If such case, it would be nice if the build process would have an optional extra step to gzip the assets and that probably means to replace automatically the reference to the assets within the index.html to use the .gz extension.

Since reate-react-app is in charge of injecting the javascript file reference into index.html and since nobody likes to eject, it would seem like a built-in build step should be added for the case I've described.