improve README (#14)

README.md

@@ -1,13 +1,18 @@
 # PPA
 SecureDNA is a free, non-profit screening platform designed to safeguard DNA synthesis everywhere.
 
-This is a PPA repository for the SecureDNA client and related utilities.  Currently built for Ubuntu amd64 and arm64, and tested in 22.04 and later.
+This is a PPA repository for the SecureDNA client and related utilities.  Currently built for amd64 (Ubuntu 22.04 and later) and arm64 (Debian Bookworm and later).
 
-- You can find information about the project as a whole, including papers and a live demo, at the [main site](https://securedna.org).
+## Overview
+
+- You can find information about the project as a whole, including [papers](https://securedna.org/research) and a [live demo](https://securedna.org/demo/), at the [main site](https://securedna.org).
 - To use the client with real databases, you'll need to [obtain certificates](https://securedna.org/start/) using utilities in this PPA.
-- Source code for the client and utilities, and for the servers it talks to, is available in our [monorepo](https://github.com/SecureDNA/SecureDNA).
+- Docker/podman container images are also available:
+  - As a minimal-size image containing just `synthclient`: `docker pull ghcr.io/securedna/synthclient`
+  - As an image containing both `synthclient` and the tools required to request a certificate and generate authorization tokens: `docker pull ghcr.io/securedna/synthclient-tools`
+- Source for the client and servers is available in our [monorepo](https://github.com/SecureDNA/SecureDNA).
 
-# Usage
+## Adding the PPA to your system and installing its contents
 
 ```bash
 curl -sSL https://securedna.github.io/ppa/deb/securedna-keyring.gpg | sudo tee /usr/share/keyrings/securedna-keyring.gpg > /dev/null