Add basic usage documentation

docs/index.rst

@@ -15,6 +15,7 @@ Contents:
 
    overview
    install
+   usage
 
 
 Indices and tables

docs/usage.rst

+Usage
+=====
+
+snf-image-creator comes in 2 variants:
+ * snf-mkimage: A user-friendly dialog-based program
+ * snf-image-creator: A non-interactive command line program
+
+Creating a new image
+--------------------
+
+Suppose you want to create a new ubuntu server image. Download the installation
+disk from the internet:
+
+.. code-block:: console
+
+   $ wget http://ubuntureleases.tsl.gr/12.04.1/ubuntu-12.04.1-server-amd64.iso
+
+Create a 2G sparce file to host the new system:
+
+.. code-block:: console
+
+   $ truncate -s 2G ubuntu_hd.raw
+
+And install the ubuntu system on this file:
+
+.. code-block:: console
+
+   $ sudo kvm -boot d -drive file=ubuntu_hd.raw,format=raw,cache=none,if=virtio \
+     -cdrom ubuntu-12.04.1-server-amd64.iso
+
+After this, become root, activate the virtual environment you have installed
+snf-image-creator in, and use *snf-mkimage* to create and upload the image:
+
+.. code-block:: console
+
+   $ sudo -s
+   $ source /path/to/snf-image-env/bin/activate
+   $ snf-mkimage ubuntu_hd.raw
+
+In the first screen you will be asked to choose if you want to run the program
+in *Wizand* or *Expert* mode. Choose *Wizard*.
+
+.. image:: /snapshots/01_wizard.png
+
+Then you will be asked to provide a name, a description, an ~okeanos account
+and the token corresponding to this account. After that you will be asked to
+confirm the provided data.
+
+.. image:: /snapshots/06_confirm.png
+
+Choosing *YES* will create the image and upload it to your ~okeanos account.