Update README

[garoevans]

Update the readme to follow a better format: http://docs.writethedocs.org/en/latest/writing/beginners-guide-to-docs/#id1

[JayOwl]

Trying to get your example code to work, using the scope resolution operator didn't work when trying to set the variable return type to the set string. ($aFruit->is(Fruit::APPLE))

The equals operator used in the in the SplEnum documentation worked. (Fruit::APPLE == $aFruit)

Thanks!