Initial implementation for acpush

Currently supports performing meta discovery to find appropriate
endpoint, and pushing provided image and signature to the server. Relies
on rkt's config files for authentication.

README.md

@@ -2,4 +2,42 @@
 
 experimental implementation of the proposed push specification for ACIs
 
-See https://github.com/appc/spec/issues/418 for details of the proposed specification.
+See https://github.com/appc/spec/issues/418 for details of the proposed
+specification.
+
+## Usage
+It takes as input an
+[ACI](https://github.com/appc/spec/blob/master/SPEC.md#app-container-image)
+file, an
+[ASC](https://github.com/coreos/rkt/blob/master/Documentation/signing-and-verification-guide.md)
+file, and an [App Container
+Name](https://github.com/appc/spec/blob/master/spec/types.md#ac-name-type) (i.e.
+`quay.io/coreos/etcd`). Meta discovery is performed via the provided name to
+determine where to push the image to.
+
+See `acpush --help` for details on accepted flags.
+
+## Build
+
+Building acpush requires go to be installed on the system. With that, the
+project can be built with either:
+
+```
+go get github.com/appc/acpush
+```
+
+or
+
+```
+git clone https://github.com/appc/acpush.git
+cd acpush
+go get -d ./...
+go build
+```
+
+## Auth
+
+acpush reads rkt's config files to determine what authentication is necessary
+for the push. See [rkt's
+documentation](https://coreos.com/rkt/docs/latest/configuration.html) for
+details on the location and contents of these configs.