update readme

README.md

@@ -2,6 +2,29 @@
 
 Uses [SSMTP](https://packages.debian.org/stable/mail/ssmtp) to send mails (for example if you have a redirect sieve rule).
 
+
+```
+create table if not exists virtual_domains (
+	id serial primary key, 
+	name text not null
+);
+
+create table if not exists virtual_users (
+	id serial primary key, 
+	domain_id integer not null references virtual_domains(id),
+	email text not null,
+	destination text not null
+);
+
+
+create table if not exists virtual_aliases (
+	id serial primary key, 
+	domain_id integer not null references virtual_domains(id),
+	source text not null,
+	destination text not null
+);
+```
+
 # Volumes
 - `/var/lib/vmail/mail`