doc: sample application user guide

The 1.7 DPDK_SampleApp_UG document in MSWord has been converted to rst format for
use with Sphinx. There is an rst file for each chapter and an index.rst file
which contains the table of contents.
The top level index file has been modified to include this guide.

This document contains some png image files. If any of thes png files are modified
they should be replaced with an svg file.

This is the fifth document from a set of 6 documents.

Signed-off-by: Bernard Iremonger <bernard.iremonger@intel.com>