docs/manual: run-tests test framework

docs/manual: run-tests test framework

This patch adds a new manual section that captures an overview
of the run-tests tool, how to manually run a test and where to
find the test case script.

A brief set of steps is included to go through how to add a new
test case and suggestions on how to test/debug.

Cc: Ricardo Martincoski <ricardo.martincoski@gmail.com>
Cc: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Matthew Weber <matthew.weber@rockwellcollins.com>
[yann.morin.1998@free.fr:
  - switch the creating and debugging sections
  - minor reformatting
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>