docs(README): usage examples and dockerhub links

.vale/Vocab/smtp/accept.txt

@@ -1,5 +1,6 @@
 aws|AWS
 certbot
 cloudflare|Cloudflare
+dockerhub|DockerHub
 dkim|DKIM
 env|Env

README.md

@@ -2,6 +2,33 @@
 
 Wraps [cisagov/postfix-docker](https://github.com/cisagov/postfix-docker) in automation for generating [Let's Encrypt](https://letsencrypt.org/) SSL certificates and dkim DNS records.
 
+On DockerHub:
+
+- [docker.io/niallbyrne/smtp-aws:main](https://hub.docker.com/repository/docker/niallbyrne/smtp-aws/general)
+- [docker.io/niallbyrne/smtp-cloudflare:main](https://hub.docker.com/repository/docker/niallbyrne/smtp-cloudflare/general)
+
+## Usage Examples
+
+```bash
+docker pull docker.io/niallbyrne/smtp-aws:main
+docker run -v \
+  $(pwd)/certs:/etc/letsencrypt/live/ \
+  $(pwd)/aws.env:/mnt/aws.env \
+  -e ENV_FILE=/mnt/aws.env \
+  docker.io/niallbyrne/smtp-aws:main
+```
+
+or
+
+```bash
+docker pull docker.io/niallbyrne/smtp-cloudflare:main
+docker run -v \
+  $(pwd)/certs:/etc/letsencrypt/live \
+  $(pwd)/cloudflare.env:/mnt/cloudflare.env \
+  -e ENV_FILE=/mnt/cloudflare.env \
+  docker.io/niallbyrne/smtp-cloudflare:main
+```
+
 ## Build Arguments
 
 | Name     | Value                                         | Default |