Add small script to setup label in lesson repo

@gvwilson Do you approve this?

@willingc If @gvwilson approve this, could you review it?
GitHub will return a JSON that is meaningful for me but maybe not for novice.

In case of failure user will get something like

~~~
{
  "message": "Validation Failed",
  "documentation_url": "https://developer.github.com/v3/issues/labels/#create-a-label",
  "errors": [
    {
      "resource": "Label",
      "code": "invalid",
      "field": "color"
    }
  ]
}
~~~

and in case of success

~~~
{
  "url": "https://api.github.com/repos/r-gaia-cs/bc/labels/getting-started",
  "name": "getting-started",
  "color": "fbca04"
}
~~~