Add lazy load example

[flying-sheep]

I wrote an example component able to lazy load languages to avoid bundling everything: https://codesandbox.io/s/lazy-load-prism-react-renderer-2g7qhh

Doesn’t support language aliases, only the language names used in the filename (e.g. bash, but not shell or sh, since the file is called prism-bash.js)

You might want to link it (or a fork you control) from the readme.