Add comprehensive macOS build and run instructions

Add example output section showing Mesa GPU execution

Clarify that sqrt() is an OpenCL C built-in function, not a libclc function

Document RUSTICL_ENABLE requirement for Mesa GPU example

Split Mesa example into separate GPU and CPU binaries

Add Mesa OpenCL example program

Explain why libclc installation isn't required

Replace deprecated clCreateCommandQueue with clCreateCommandQueueWithProperties

Fix CL_TARGET_OPENCL_VERSION warning by defining OpenCL 3.0 target

Add detailed explanation of libclc to README

Add OpenCL installation instructions and better error messages

Initial commit: OpenCL Hello World with libclc math functions