added a small comment. just a beginning for issue #1

installer.cfg

@@ -3,8 +3,9 @@ tls_key_file = /etc/ssl/private/ssl-cert-snakeoil.key
 tls_cert_file = /etc/ssl/certs/ssl-cert-snakeoil.pem
 
 [database]
+# Select database engine : postgres or mysql
+engine = postgres
 host = 127.0.0.1
-engine = postgres 
 install = true
 
 [postgres]