Signed-off-by: Jessica Yao <jessica@heptio.com>

ksonnet.next isn't released yet. This message remained as a port from
the original README file in the kubecfg project.

This commit is a follow-up to the discussion in the ksonnet.next design
doc, in which users consistently expressed their preference that the
`update` command be called `apply`.

NOTE: We have renamed `pkg/kubecfg/update_test.go` ->
`pkg/kubecfg/apply_test.go`, but we copy the `update`'s integration test
file. The reason is that the `update` unit tests actually test things
like GC (rather than the command itself), so the file name is
inconsequential. On the other hand, the integration tests test the
commands themselves, so it is important to have two copies, one for
`update` and one for `apply`.

Now the commands take either an env or a file, so let's at least fix the
README to make it work with files.

- `gofmt -s utils/registry_test.go`
- Fix missing `if err != nil` check in `cmd/delete.go` (a bug, but not critical)
- Add goreportcard button to README

Remove poor attempt at setup step entirely.  This makes the actual
quickstart content more obvious ... and anyone who _actually_ wants to
run it will already know how to checkout a git repo.

Update example to use something self-contained.

Add diff,delete to the quickstart example

Fixes #12

- Add travis build status badge
- Update description of current status
- Add note about upstream golang OSX+cgo issue with <1.8.1

s/go install/go get/