Support for all XO models

Each XO model requires a OS image specifically built. The
open firmware command for flashing the OS image are identical
between models, with the exception of the XO-1. Therefore, it
could be a problem to have a script that does not consider this
fact. ie., plugin the XO4 USB stick in a XO1.75.

This patch uses a already known name convention for OS images,
detects the XO model, and runs the update command with the proper
OS image.

This is also useful for having a universal update stick. ie., one
stick that can safely upgrade all XO versions.

Signed-off-by: Martin Abente Lahaye <tch@sugarlabs.org>
Update README

Fix concepts and update instructions.

Signed-off-by: Martin Abente Lahaye <tch@sugarlabs.org>
Move script to the proper directory

Since the directory of this script is crucial, it would
be better to just have it in the right place from the
beginning.

Signed-off-by: Martin Abente Lahaye <tch@sugarlabs.org>
Update instructions

Simplify instructions.

Signed-off-by: Martin Abente Lahaye <tch@sugarlabs.org>
Fix terminology

In the OLPC linguo, firmware tends to identify the open
firmware, while for the OS the Image or Build are prefered.

Signed-off-by: Martin Abente Lahaye <tch@sugarlabs.org>
Merge pull request #1 from tchx84/improvements

Improvements