Add Documentation Links

[jonshern]

Wanted to get this package added to awesome go but it is missing a couple of things in the Readme

godoc link to the repo
coverage service link to the repo
goreportcard link to the repo

[auyer]

I agree this package deserves to be in Awesome, and I can help you with that @guregu

The parts I can not are setting up the integration between your CI and Coverage tool. I see you have a CircleCI file, but its either private or not working.
If you'd like, I can add the goreportcard, CI and Coverage badges, and the CircleCI configuration. You would just need to connect the accounts !
This repo of mine have such things and you can give it a look : auyer/steganography.