Added the content for MD-SAL to the Developer's Guide

This is the original patch from Sujatha modified by Colin Dixon to build.

Change-Id: I0389dfdfda786d1865b7fc88535d70cfedb66aea
Signed-off-by: Sujatha Joseph <josephs@brocade.com>
Signed-off-by: Colin Dixon <colin@colindixon.com>
Merge "Added the content for MD-SAL to the Developer's Guide"