Clarify the link with react-share

[tttp]

Hi,

Am I right to think next-share started as a fork of react-share and then got improved/added new features?

I'm pretty sure the MIT license allows it, but it would be nice to clarify the origin and possibly explain if the migration is as trivial as switching the import name or if there are other changes.

talking about changes, would be awesome to highlight what your version fixes (or what PR you accepted, there are tons waiting on react-share)