message: added basic flag info for OpenCL
diff: @@ -629,7 +629,26 @@ enabled.
  \subsection{OpenCL}
  -OpenCL in \CmdStan enables Cholesky decompositions to utilize a GPU for large parallel computations. Please refer to \url{https://github.com/stan-dev/math/wiki/OpenCL-GPU-Routines} for setup instructions. Currently, OpenCL will only pass matrices over to the GPU if their dimensions are larger than 1250x1250.
  +OpenCL in \CmdStan enables Cholesky decompositions to utilize a GPU for large parallel computations. In order to use OpenCL, a few lines need to be added to \code{make/local}.
  +\begin{itemize}
  + \item \Verb|STAN_OPENCL=true| Enable the use of OpenCL.
  + \item \Verb|OPENCL_PLATFORM_ID=<int>| Set which OpenCL platform to use.
  + \item \Verb|OPENCL_DEVICE_ID=<int>| Set which OpenCL device on the selected platform to use.
  +\end{itemize}
  +
  +Windows users need to additionally specify the following two flags depending on the GPU you are running OpenCL on.
  +
  +\subsubsection{NVIDIA GPU}
  +\begin{itemize}
  + \item \Verb|LDFLAGS_OPENCL= -L"\$(CUDA_PATH)\lib\x64" -lOpenCL|
  +\end{itemize}
  +
  +\subsubsection{AMD GPU}
  +\begin{itemize}
  + \item \Verb|LDFLAGS_OPENCL= -L"\$(AMDAPPSDKROOT)lib\x86_64" -lOpenCL|
  +\end{itemize}
  +
  +If you are unsure if your devices support OpenCL, we suggest running the \code{clinfo} application that lists all available OpenCL supported devices. Please refer to \url{https://github.com/stan-dev/math/wiki/OpenCL-GPU-Routines} for additional setup instructions. Currently, OpenCL will only pass matrices over to the GPU if their dimensions are larger than $1250\times 1250$.
  \section{Optional Components for Developers}
  