Add some documentation (global README) -- WIP

README.md

-Varnish Ingress Controller
---------------------------
+# Varnish Ingress Controller
 
-This is an implementation of a [kubernetes Ingress controller](https://kubernetes.io/docs/concepts/services-networking/ingress/)
+This is an implementation of a [Kubernetes Ingress controller](https://kubernetes.io/docs/concepts/services-networking/ingress/)
 based on [Varnish](http://www.varnish-cache.org).
 
-NOTE: WORK IN PROGRESS
+The present documentation presupposes familiarity with both Kubernetes and
+Varnish. For more information, see:
 
+* Kubernetes: https://kubernetes.io/
+* Varnish: http://www.varnish-cache.org
+
+## WORK IN PROGRESS
+
+The Ingress controller implementation is presently under development
+as a minimum viable product (MVP) and is undergoing initial testing. It is
+currently subject to a number of limitations, expected to be removed over
+time, including:
+
+* No support for TLS connections
+* The controller only attends to definitions (Ingresses, Services and
+  Endpoints) in the namespace of the Pod in which it is deployed.
+* Only one Ingress definition is valid at a time. If more than one definition
+  is added to the namespace, then the most recent definition becomes valid.
+* A variety of elements in the Varnish implementation of Ingress are
+  hard-wired, as detailed of the following, and are expected to become
+  configurable in further development.
+
+# Installation
+
+The container image implementing the Ingress, including the Ingress
+controller deployed in the same container, is created via a
+multi-stage Docker build using the Dockerfile in the root of the
+source repository. The build can be initiated with the ``container``
+target for ``make``:
+
+```
+$ make container
+```
+
+If you wish to add custom options for the Docker build, assign these
+to the environment variable ``DOCKER_BUILD_OPTIONS``:
+
+```
+$ DOCKER_BUILD_OPTIONS='--no-cache --pull' make container
+```
+
+The resulting image must then be pushed to a registry available to the
+Kubernetes cluster.
+
+The Ingress can then be deployed by any of the means that are
+customary for Kubernetes. The [``deploy/``](deploy/) folder contains YAML
+configurations for one of the ways to deploy an Ingress.
+
+The [``example/``](example/) folder contains YAML configurations for
+sample Services and an Ingress to test and demonstrate the Ingress
+implementation (based on the "cafe" example from other projects).