[BUGID# 293] - documentation/poky-ref-manual/extendpoky.xml: Added text for choosing server
[BUGID# 293] - I added text at the end of section 3.2.3 "Customizing Images
Using Custom IMAGE_FEATURES" to include explanation of the two servers
Poky uses for images by default. Also how to change the variable
IMAGE_FEATURES to configure the server. This change is part of the
fix for BUGID# 293 and was suggested by Scott Garman.
Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
