Add some additional detail to the API docs

Many of the examples used by the V2 API docs for authorization are written as

headers: {authorization: 'Basic REPLACE_BASIC_AUTH'}

Links are provided to a dedicated page regarding authentication, but all that currently states is

HTTP basic authentication. The username should be set as the circle-token value, and the password should be left blank. Note that project tokens are currently not supported on API v2.

It would be rather helpful if it could also detail the fact that

  • what the circle-token is and where it can be generated.
  • the fact that it is base64 encoded
  • the fact that a : must be appended to the circle-token before the resulting string is encoded.

The last one is something of a trip hazard as it must come from the fact that normally details would be passed in the form username:password but as you are using tokens the password is blank.