Update library description

[deandreamatias]

In this line say 'An incomplete library'
Maybe can update this to:

A dart library for interfacing with the Spotify API.

If this library is under construction, maybe indicate in README

[hayribakici]

Maybe we should create another issue for that?

[rinukkusu]

I'm not entirley sure what the problem seems to be. The discrepancy between the description in the pubspec.yaml and the README?

To be factually correct: the library is incomplete and back then I wanted to let people know. Right now we probably already cover most of the common use cases, but still are far from complete. Maybe we could add a section in the README or Wiki with all the endpoints that are currently implemented?

[hayribakici]

Oops it seems like I posted into the wrong issue. I meant to create another issue regarding #75. Sorry.
Nevertheless, a list of supported endpoints sounds like a good idea.

[deandreamatias]

If library is incomplete yet, then this isn't a issue