docs: update readme

README.md

@@ -4,6 +4,24 @@ This is a very simple web & SMTP server which will response to all requests sent
 
 ## Usage
 
+Start the server with the following:
+
 ```
-blackhole
+docker run --pull always \
+           -p 80:8080 \
+           -p 25:2525 \
+           ghcr.io/postalserver/blackhole:latest
 ```
+
+### SMTP
+
+You can send email to `[email protected]` which will be accepted. Any other username will be blocked at the `RCPT TO` stage.
+
+### HTTP
+
+The following URLs are available. 
+
+* `/200` - returns a 200 OK
+* `/403` - returns a 403 Forbidden
+* `/500` - returns a 500 Internal Server Error
+* All other URLs will return a 404 Not Found