Moved the Poky image file to the "Figures" folder.

The image file was in the same directory as the main reference manual
files.  So I moved the file into subdirectory "Figures" with other
figures.

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>

diff --git a/documentation/poky-ref-manual/poky-ref-manual.png b/documentation/poky-ref-manual/figures/poky-ref-manual.png
similarity index 100%
rename from documentation/poky-ref-manual/poky-ref-manual.png
rename to documentation/poky-ref-manual/figures/poky-ref-manual.png