Added README

README.md

+# Prerequisites
+
+* Supported operating systems:
+  * Linux
+  * Mac OS X
+  * Windows (via cross-compilation on Linux using MinGW)
+* Supported GPUs:
+  * AMD GPU with installed drivers
+  * NVIDIA GPU with installed drivers
+* Supported OpenCL SDKs:
+  * AMD APP SDK: installation root exported in environment variable `AMDAPPSDKROOT `
+  * NVIDIA CUDA Toolkit: installation root exported in environment variable `NVIDIA_SDK_INSTALL_PATH`
+
+# Build instructions
+
+The codebase contains a top-level Makefile that builds the library and the example, providing the following build targets:
+
+* linux (default)
+* macos
+* win32
+* win64
+* clean
+
+# Usage
+
+* Library
+* Example