Docs: Update the tutorial to use GitHub's API

I had the pleasure of coming across jq on the internet. I jumped into the tutorial full of excitement, only to be met with this:

```json
{
  "errors": [
    {
      "code": 68,
      "message": "The Twitter REST API v1 is no longer active. Please migrate to API v1.1. https://dev.twitter.com/docs/api/1.1/overview."
    }
  ]
}
```

That made me kind of sad, and isn't the nicest way to be introduced to jq. So, I thought of a good, developer friendly API that probably won't turn off anytime soon, and chose GitHub. I rewrote the tutorial to fit GitHub – I'm not sure if I hit all the features you are attempting to show off in the Twitter tutorial, and there is some additional complexity due to the data returned, but overall I *think* it does a pretty good job of showing the power of jq.

One small caveat – I had all sorts of trouble on my machine getting bonsai to cooperate with me...so there may be some syntax issues with the yaml rendering.

Ya! Let me know what you think. :)