Added a note about OpenSubdiv

Author: betajippity

README.md

@@ -36,6 +36,7 @@ Notes:
 * Nuparu does not contain the entirety of Boost; instead, only a subset of Boost required for OpenVDB is included. The components of Boost included are header-only.
 * OpenVDB has a slight modification in Coord.h for Windows support
 * RMSD has minor modifications for C++ support
+* OpenSubdiv is built with Ptex and TBB support only. Other backends, such as OpenCL, are not included.
 * All binary OSX libraries are built with OSX's Clang variant (Apple LLVM 5.1 or greater) using libc++.
 * All binary Windows libraries are built using /MT with Visual Studio 2013, except for OpenVDB, which is build using /MT with Visual Studio 2012. OpenVDB will be updated soon.
 * All binary libraries on all platforms are built for x86-64