docs(docker): basic usage instructions

docker/README.md

+# Aurweb and Docker
+
+The `INSTALL` document details a manual Aurweb setup, but Docker images are also
+provided here to avoid the complications of database configuration (and so
+forth).
+
+### Setup
+
+Naturally, both `docker` and `docker-compose` must be installed, and your Docker
+service must be started:
+
+```sh
+systemctl start docker.service
+```
+
+The main image - `aurweb` - must be built manually:
+
+```sh
+docker compose build aurweb-image
+```
+
+### Starting and Stopping the Services
+
+With the above steps complete, you can bring up an initial cluster:
+
+```sh
+docker compose up
+```
+
+Subsequent runs will be done with `start` instead of `up`. The cluster can be
+stopped with `docker compose stop`.
+
+### Testing
+
+With a running cluster, execute the following in a new terminal:
+
+```sh
+docker compose run test
+```