Add installation instruction file;

Order directories.

rivista/xmpp/instance.py

@@ -0,0 +1,11 @@
+#!/usr/bin/python
+# -*- coding: utf-8 -*-
+
+from slixmpp import ClientXMPP
+
+class XmppInstance(ClientXMPP):
+    def __init__(self, jid, password):
+        super().__init__(jid, password)
+        self.register_plugin('xep_0060')
+        self.connect()
+        # self.process(forever=False)