Added README.md file

README.md

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+OpenCL C++ Standard Library Instructions
+================================================
+
+The instructions how to build SPIR-V generator/Clang can be found here:
+  https://github.com/KhronosGroup/SPIR/tree/spirv-1.1
+
+-----------------------------------
+Step 1: OpenCL C++ standard library
+-----------------------------------
+
+To clone the OpenCL C++ standard libary use the following cmdline:
+
+```bash
+  git clone https://github.com/KhronosGroup/libclcxx.git master
+```
+
+--------------------------------
+Step 2: Creating SPIR-V binaries
+--------------------------------
+
+To create a SPIR-V binary from a valid OpenCL-C file (.cl), use the following
+command lines:
+
+```bash
+  clang -cc1 -emit-spirv -triple <triple> -cl-std=c++ -I <libclcxx dir> -x cl -o <output> <input>
+```
+
+Notes:
+
+* `<triple>`: for 32 bit SPIR-V use spir-unknown-unknown, for 64 bit SPIR-V use spir64-unknown-unknown.
+* -D<extension>: to enable support for extension. e.g. -Dcl_khr_mipmap_image compile option will enable mipmap support.
+* -cl-fp16-enable: to enable half support and define cl_khr_fp16
+* -cl-fp64-enable: to enable double support and define cl_khr_fp64
+* -O<optimization level>: -O0 (default) is the only tested option value at the moment. It's assumed by design that all optimizations are executed by SPIR-V consumer
+* `<libclcxx dir>`: path to include directory from libclcxx (https://github.com/KhronosGroup/libclcxx)
+.
+
+```bash
+  clang -cc1 -emit-spirv -triple=spir-unknown-unknown -cl-std=c++ -I include kernel.cl -o kernel.spir
+```
+
+----------------
+Reporting issues
+----------------
+
+Bugs/feature requests can be filed via [github](https://github.com/KhronosGroup/SPIR/issues) or [Khronos Bugzilla](https://www.khronos.org/bugzilla/) bug tracker.