Update README.md

[seanreed1111]

updates readme. Seems like usage changed over the years from builder = pjs.ObjectBuilder(examples['Example Schema'])

to

builder = pjs.ObjectBuilder(examples)

The former gives the following error:

`KeyError Traceback (most recent call last) in <cell line: 2>() 1 import python_jsonschema_objects as pjs ----> 2 builder = pjs.ObjectBuilder(example["Example Schema"]) 3 ns = builder.build_classes() 4 Person = ns.ExampleSchema 5 james = Person(firstName="James", lastName="Bond")

KeyError: 'Example Schema'`