Fixed wording on how the OpenEmbedded build system dynamically
generates do_image_* tasks as needed during image generation.
(From yocto-docs rev: 9df98d77a446cd5d27c4e87418117a904b1f4231)
Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>