Update readme
Update readme

- Remove out of date usage example
- Add link to docs on godoc
- Update go dependency to v1.7+

[#132289909]

Signed-off-by: Josh Hill <d8b194a1fc06171ecd965621d47d83f9b6bf4885@pivotal.io>

pivotal-cf/brokerapi,pivotal-cf/brokerapi,drnic/brokerapi