IACO-527: GitHub documentation

It would probably be best to read the documentation instead of looking at the markdown, so feel free to open up the following links:
https://github.com/yuval-netanel/inapp-ios/tree/IACO-527-github-documentation
https://github.com/yuval-netanel/inapp-ios/blob/IACO-527-github-documentation/doc/integration.md

As a semi-outsider, you should definitely give this a glance, @rauchy.
Just use http://developers.klarna.com already now.