Add exemple with private github

[kosssi]

Thanks for this project.

I test it now but I have question it's possible to use it with a private github ?

[azproduction]

In current implementation plato-as-service downloads zip using public url. But that could be updated to use API V3: https://developer.github.com/v3/repos/contents/#get-archive-link

$ curl -H "Authorization: token ab499f3b..." \
-L https://api.github.com/repos/godzilla/my_priv_repo/zipball > wut.zip

This implementation requires OAuth token from service consumer.

Url schema could be:

/:user/:repo/:branch/?oauth_token=ab499f3b...

[azproduction]

@kosssi PR is pending