docs: browsers support

[samerset-rmn]

Hi!

I really like this library, but I can't find out which browsers it supports and which it doesn't. My guess is that support for older browsers is not a primary goal here, and I understand that. But it would be great to have this information somewhere in the docs – a list of supported browsers or a note warning about it.

[raon0211]

Yes, it should be supported in browsers that support ES6, as long as there's proper polyfill support. However, I think we should check the browser compatibility to be sure.