Tools: Added manual to use GstShark for tracing & profiling

Tools: Added manual to use GstShark for tracing & profiling

This commit is to add a manual to use a GstShark tool to support
tracing and profiling method.

GstShark is an open-source project from Ridgerun that provides
benchmarks and profiling tools for GStreamer 1.7.1 (and above).
It includes tracers for generating debug information plus some tools
to analyze the debug information.

**Changes proposed in this PR:**
1. Added how to use GstShark
2. Updated GST_DEBUG_DUMP_DOT_DIR usage for debugging

Signed-off-by: Geunsik Lim <geunsik.lim@samsung.com>