tests: dynappsrc: explain more about test case
tests: dynappsrc: explain more about test case

Change-Id: Ic64bcde61e94c182a920acc45d7211116761433b
Reviewed-on: https://gpro.palm.com/30368
Reviewed-by: Wonchul Lee <9841bdbec9dbb2acc2dcaaa1dab0491399f0e464@lge.com>
Reviewed-by: Jeongseok Kim <0c03ab7a1b32f29697716389c3f9549845834271@lge.com>
Tested-by: Jeongseok Kim <0c03ab7a1b32f29697716389c3f9549845834271@lge.com>

justinjoy/gst-plugins-lp,justinjoy/gst-plugins-lp