Added Documentation on how upgrading suse image

updating_suse_image.rst

+How to update you old Suse Image (Suse 12.1 or sooner)
+******************************************************
+
+Procedure
+---------
+
+Run this whole command as root
+++++++++++++++++++++++++++++++
+
+# wget http://perso.telecom-paristech.fr/~leninivi/slapprepare.tar.gz ;zypper remove -y slapos.node ; rm /etc/opt/slapos/slapos.node-0.88-28.1.x86_64.rpm ;tar -xzf slapprepare.tar.gz ; cd slapprepare; python setup.py install; cd .. ; rm -r slapprepare* ; slapprepare -u
+
+Check your config
+-----------------
+
+Check your config file and your cron file
++++++++++++++++++++++++++++++++++++++++++
+Run:
+# slaptest
+This script will check your config file for missing section or parameters
+
+You can use the slapos.cfg.example config file as reference.
+http://git.erp5.org/gitweb/slapos.core.git/blob_plain/HEAD:/slapos.cfg.example
+
+
+Check dedicated cron file
++++++++++++++++++++++++++
+
+# less /etc/cron.d/slapos
+
+It should contain a call to slapupdate
+
+Check your configuration directory
+++++++++++++++++++++++++++++++++++
+
+# ls /etc/opt/slapos/
+
+It should only contain your slapos configuration files and *-needed files
+
+Configuring your machine:
+-------------------------
+
+LXC
+++++
+If you want to run lxc on you machine run these command:
+
+# touch /etc/opt/slapos/SlapContainer-needed ; systemctl restart slapos-boot-dedicated.service
+
+openvpn
++++++++
+Openvpn by vifib for ipv6 is forced by default in the package.
+If you want to deactivate it run
+
+# rm /etc/opt/slapos/openvpn-needed
+