Define a README for /src subdir

Signed-off-by: coleramos425 <colramos@amd.com>

src/README.md

@@ -0,0 +1,6 @@
+This directory contains all the source code files for the Omniperf project.
+The top-level `omniperf` executable is the entry point and defines the flow for subsequent execution modes.
+
+To build Omniperf as a developer (from source) please add this directory to `PATH`.
+You will find utilities and logic specific to Omniperf's different execution modes in their
+respective subdirectories.