Add changelog

[ryb73]

First, thanks for this helpful module!

There have recently been major version upgrades, but it's not clear what the changes were. Is it safe to upgrade? A CHANGELOG.md or equivalent would make this library easier to use.

[niftylettuce]

It's much easier to just use np when you publish new versions, as it will create a new Release in the GitHub Releases tab, and automatically populate a list of all the changes for you since the last version was published. It's super easy to read through the Releases tab to see new major versions and differences.

https://github.com/sindresorhus/np

[JounQin]

No changelog nor GitHub release...

cc @mathiasbynens