Add some examples and usage details in the readme.

[bsutton]

Just came across this project.
Its a little too hard to start using as I'm having to read code on git to see what it does and doesn't do.

Some example usages in the readme would help potential users evaluate if it will suit their purpose and speed up the process of integrating your package into a project.

[juandelgado]

In case someone swings by, I've opened a PR with a very simple addition to the README on how to use the library, see dart-archive/pubspec_parse#87.

Hope it helps.

[Laur1nMartins]

Having that really helps! Hopefully this will be added to the readme.