Reflect change to Postgres in README

README.textile

 * Mobile push notifications via "Z-Push":http://z-push.sourceforge.net/soswp/index.php?pages_id=1&t=home.
 * Jabber/"XMPP":http://xmpp.org/ instant messaging via "Prosody":http://prosody.im/.
 * An RSS Reader via "Selfoss":http://selfoss.aditu.de/.
-* Virtual domains for your email, backed by "MySQL":https://www.mysql.com/.
+* Virtual domains for your email, backed by "PostgreSQL":http://www.postgresql.org/.
 * Secure on-disk storage for email and more via "EncFS":http://www.arg0.net/encfs.
 * Spam fighting via "DSPAM":http://dspam.sourceforge.net/ and "Postgrey":http://postgrey.schweikert.ch/.
 * Mail server verification via "OpenDKIM":http://www.opendkim.org/, so folks know you're legit.