Fixes [YOCTO #8439]
The "image-swab" class depends on "strace" package being on
the build host. I added that fact to the note where we say
the class is not maintained.
(From yocto-docs rev: 503f4199b3c0bcfcd333dbab025b40f9508a6820)
Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>