Update readme.

README.md

 # portabledsb
 A portable c++ version of the AllJoyn DSB
 
-https://git.allseenalliance.org/cgit/dsb.git/
+
+The AllSeen Alliance has a Device System Bridge (DSB), which allows non-allseen devices to
+communicate on an AllJoyn bus. There's a good document describing the software here:
+
+  https://git.allseenalliance.org/cgit/dsb.git/plain/Docs/AllJoyn%20-%20Device%20System%20Bridge%20-%20Whitepaper%20v1.0.pdf
+
+The code was contributed by Microsoft and is writting using c++/cx (WinRT). This project's
+goal is to re-create that software in std c++ so that it can be run on Windows, Linux, and
+Mac. 
+
+The WinRT version is here:
+
+  https://git.allseenalliance.org/cgit/dsb.git/