Outdated section on README regarding Custom Scroll Restoration API

[benmccann]

The README says:

This problem can get solved when the Custom Scroll Restoration API gets widely implemented:

https://code.google.com/p/chromium/issues/detail?id=477353
http://majido.github.io/scroll-restoration-proposal

It looks to me like this has been implemented, so this text should probably be updated a bit

[waynebloss]

I came here because the browser implementation was actually not working for me. Perhaps I'm doing something else wrong, but I'm going to apply this polyfill until I figure it out.