Create update.md

docs/update.md

+In order to update your ravada, you have to do a few
+steps from the install and production documents that
+we will show here.
+
+
+# Steps for a clean update
+
+Step 1: Download the _deb_ package of the new version
+        found at the [UPC ETSETB repository](http://infoteleco.upc.edu/img/debian/).
+
+Step 2: Install the _deb_ package.
+
+    $ sudo dpkg -i ravada_0.1.2_all.deb
+    
+Step 3: Reconfigurate the systemd.
+
+    $ sudo systemctl daemon-reload
+    $ sudo systemctl enable rvd_back
+    $ sudo systemctl enable rvd_front
+    
+Step 4: Start the services.
+
+    $ sudo systemctl start rvd_back
+    $ sudo systemctl start rvd_front
+