Added support for Mysql SSL connection

doc/config.markdown

@@ -87,6 +87,15 @@ define('DB_NAME', 'kanboard');
 
 // Mysql/Postgres custom port (null = default port)
 define('DB_PORT', null);
+
+// Mysql SSL key
+define('DB_SSL_KEY', null);
+
+// Mysql SSL certificate
+define('DB_SSL_CERT', null);
+
+// Mysql SSL CA
+define('DB_SSL_CA', null);
 ```
 
 LDAP settings