badges: more badges for great health

Adding the Go report card badge. Signed-off-by: Stephen J Day <stephen.day@docker.com>

readme: add link to GoDoc in prose

Upon further examination, the GoDoc is a very good source of documentation for this package. Send users there for now. Signed-off-by: Stephen J Day <stephen.day@docker.com>

badge: add nice badges for good health

A good open source project is measured by the number of badges at the top of the README. For now, we have two, but you have to start somewhere. Signed-off-by: Stephen J Day <stephen.day@docker.com>

Fix copyright statement

Removes placeholder, and adds basic copyright/license section to the README Signed-off-by: Sebastiaan van Stijn <github@gone.nl>