Update README.md

[intelliot]

No description provided.

[ceeK]

Thanks @intelliot, I've now incorporated your changes into the README. Apologies that I didn't merge this PR directly; this was mainly due to your second example:

Use `Date()` for the sunrise and sunset for today

This is done via a default argument in the Swift initialiser, so isn't necessary in this example. I.e. Solar(coordinate: CLLocationCoordinate2D(latitude: 51.528308, longitude: -0.1340267)) does the same thing.