Add basic use in README.md

[james-mcparlane-deltatre]

Sometimes modules don't use the name you expect them to.

Your examples use art but the name is ascii-art.

I had to search in your code to solve this riddle.

var art = require('ascii-art');

[khrome]

Sorry this was a point of confusion, I'll add some notes that cover the various allowed methods of import as it moves to 3.0

Thanks for the suggestion and for finding the library useful!