README: First stab at a useful README

* Explains how I expect things to work.

README.md

@@ -1,4 +1,43 @@
-docker-aosp
-===========
+Android Open Source Project Docker Build Environment
+====================================================
 
-Minimum Docker image to build Android AOSP
+The goal of this Docker image is to maintain a minimal build environment for
+AOSP.
+
+Developers can use the Docker image to build directly while running the
+distribution of choice, without having to worry about breaking the AOSP build
+due to package updates as is sometimes common on rolling distributions like
+Arch Linux.
+
+Production build servers and integration test servers should also use the same
+Docker image and environment. This eliminate most surprises in breakages by
+by empowering developers and production builds to use the exact same
+environment.  The hope is that breakages will be caught earlier by the devs.
+
+
+How it Works
+------------
+
+The Dockerfile contains the minimal packages necessary to build Android based
+on the main Ubuntu base image.
+
+The `aosp` wrapper is a simple wrapper to simplify invocation of the Docker
+image.  The wrapper ensures that a volume mount is accessible and has valid
+permissions for the `aosp` user in the Docker image (this unfortunately
+requires sudo).  It also forwards an ssh-agent in to the Docker container
+so that private git repositories can be accessed if needed.
+
+The intention is to use `aosp` to prefix all commands one would run in the
+Docker container.  For example to run `repo sync` in the Docker container:
+
+    aosp repo sync -j2
+
+The `aosp` wrapper doesn't work well with setting up environments, but with
+some bash magic, this can be side stepped with short little scripts.  See
+`tests/build-kitkat.sh` for an example of a complete fetch and build of AOSP.
+
+
+Tested
+------
+
+* Android Kitkat `android-4.4.4_r2.0.1`