Added sentence about version being 5.6 or greater.

Author: JeffSchering

source/install/install-ubuntu-1404-mysql.rst

@@ -3,7 +3,9 @@
 Installing MySQL Database Server
 ================================
 
-You can install either MySQL or PostgreSQL. To install PostgreSQL, see :ref:`install-ubuntu-1404-postgresql`
+You can install either MySQL or PostgreSQL. The MySQL version must be 5.6 or greater.
+
+To install PostgreSQL, see :ref:`install-ubuntu-1404-postgresql`
 
 **To install MySQL 5.6 on Ubuntu Server:**