Adds documentation that describes how to use the --offset argument in a
kickstart file
(From yocto-docs rev: 0fbb2d71fe866b4ae7721f2f70d5b50dbc019030)
Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>