README.md: Add examples and answers

README.md

@@ -29,18 +29,50 @@ want to either build images or manage garbage collection roots if you
 control the deployment host. Either of these has yet to be
 implemented.
 
-# How do I use Arion?
+# Install
 
-The command line inherits most `docker-compose` commands. These
-examples assume you're in this repo's `examples/` directory.
+Have [Nix](https://nixos.org/nix/) and Docker installed.
 
-TODO examples
+    git clone git@github.com:hercules-ci/arion.git
+    nix-env -iA arion -f .
 
-# Do I need to use Hercules CI?
+# Example of usage
+
+The command line inherits most `docker-compose` commands.
+
+    git clone git@github.com:nix-community/todomvc-nix.git
+    cd todomvc-nix/deploy/arion
+    arion up
+
+# "FAQ"
+
+### Do I need to use Hercules CI?
 
 Nope, it's just Nix and Docker Compose under the hood.
 
-# Why "Arion"?
+
+### Does Arion support Docker images?
+
+Yes, you can still specify a docker image. For example:
+
+    postgres = {
+      service.image = "postgres:10";
+      service.volumes = [ "${toString ./.}/postgres-data:/var/lib/postgresql/data" ];
+      service.environment.POSTGRES_PASSWORD = "mydefaultpass";
+    };
+
+### What about garbage collection?
+
+Arion removes the need for garbage collecting docker images,
+delegating this task to Nix.
+
+Arion creates a garbage collection root and cleans it up after
+completing the command. This means that `arion up` without `-d` is
+safe with respect to garbage collection. A deployment that is more
+serious than local development must leave a GC root on the deployment
+host. This use case is not supported as of now.
+
+### Why "Arion"?
 
 Arion comes from Greek mythology. Poseidon, the god of ~Docker~ the
 seas had his eye on Demeter. Demeter tried to trick him by disguising