[FEATURE] Add docs for deploy react native fork to npm

[gengjiawen]

Enable this will let community to make patch or share feature easily.

Related issue:
#21776
#21967

cc @kelset

[xzilja]

As far as I know npm can also install directly from github url, we might just need section in README or docs website that explains how to correctly build forked files.

@hramos posted these #21967 (comment) in one of the issues you mentioned, so thats renderer bit I guess.

[bartolkaruza]

Github dependency in package.json works fine if you commit the Android binary from installArchives. The build output is in the .gitignore, but if you remove that line you can commit the build on your branch, which then works as a Github dependency. NPM or Maven dependencies for forks require much more effort (imho), which is not worth it considering the fork should be short lived.

[kelset]

This to me seems more like an issue for the https://github.com/facebook/react-native-website repo, since that's where the docs live --> facebook/react-native-website#653.