docs: Update installation section

 * Add instructions for manually creating `/var/lib/snf-image/helper'
   directory when installing the software from source.

 * Remove instructions for installing Debian Squeeze packages (Debian
   Squeeze is no longer supported)

docs/installation.rst

@@ -2,7 +2,7 @@ Installation
 ============
 
 Before installing snf-image be sure to have a working Ganeti installation in
-your cluster. The installation process should take place in **all** ganeti
+your cluster. The installation process should take place in **all** Ganeti
 nodes. Here we will describe the installation in a single node. The process is
 identical for all nodes and should be repeated manually or automatically, e.g.,
 with puppet.
@@ -10,15 +10,9 @@ with puppet.
 Installing snf-image using packages
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-For Debian GNU/Linux and Ubuntu we provide packages in our apt repository.
+For Debian GNU/Linux and Ubuntu we provide packages in our APT repository.
 
-For Debian Squeeze add the following lines to ``/etc/apt/sources.list`` file:
-
-``deb http://apt.dev.grnet.gr squeeze/``
-
-``deb-src http://apt.dev.grnet.gr squeeze/``
-
-For Debian Wheezy add the following lines:
+For Debian Wheezy add the following lines to ``/etc/apt/sources.list`` file:
 
 ``deb http://apt.dev.grnet.gr wheezy/``
 
@@ -55,13 +49,13 @@ To install snf-image from source, download the provided source package:
 
   $ wget http://apt.dev.grnet.gr/wheezy/snf-image_<VERSION>.orig.tar.gz
 
-Untar, configure and compile the source:
+Untar, configure and build the source:
 
 .. code-block:: console
 
   $ tar -xvf snf-image_<VERSION>.orig.tar.gz
   $ cd snf-image_<VERSION>/snf-image-host
-  $ ./autoget.sh
+  $ ./autogen.sh
   $ ./configure --prefix=/usr --sysconfdir=/etc --localstatedir=/var
   $ make
 
@@ -71,6 +65,7 @@ Install snf-image:
 
   $ make install
   $ install -Dm600 defaults /etc/default/snf-image
+  $ mkdir -p /var/lib/snf-image/helper
 
 Finally, install the helper image by executing: