Getting Started Guide

@bashbaug seems to be a little shy opening issues for content discussion, so allow me to take initiative.

Following Ben's [comment](https://github.com/KhronosGroup/OpenCL-SDK/issues/1#issuecomment-628396976) on needing some Getting Started Guide (and we definitely do), let's start discussing that. He already brought up two sources to dig into.

- [The OpenGL Getting Started Guide](https://www.khronos.org/opengl/wiki/Getting_Started)
- [Troubleshooting OpenCL on Linux](https://github.com/bashbaug/OpenCLPapers/blob/master/OpenCLOnLinux.asciidoc)
- [Vulkan Guide](https://github.com/KhronosGroup/Vulkan-Guide)

And I would like to tune in with my half-baked:

- [OpenCL-Primer](https://wigner-gpu-lab.github.io/OpenCL-Primer/)
- [Anatomy of an OpenCL application](https://wigner-gpu-lab.github.io/OpenCL-Primer/Anatomy.html)
- [Getting Started on Windows using Visual Studio Code](https://wigner-gpu-lab.github.io/OpenCL-Primer/Windows.html)

I'm not sure what's the an optimal / reasonable amount of ground we should cover. I can easily finish the Windows part and cover installing compilers (MSVC and LLVM), minimal compilation from the command-line, installing IDEs (VS and VS Code), setting them up for OpenCL development. Making a similar guide for Ubuntu isn't hard either.

I too think we should follow the Vulkan Guide and stick to Markdown for its simplicity. (Not to mention not having to convert my Primer and OpenCL-KernelLoad markdowns as well, but also [SimpleOpenCLSamples](https://github.com/bashbaug/SimpleOpenCLSamples) has a fair amount of .md)

_(Note: I shamelessly promoted consuming the OpenCL SDK from a package manager, and I intend to keep doing that. (If someone has guides to consuming OpenCL headers from Conan, please drop those into the guide too.) If this SDK is going to become a living thing and we'll expose facilities for projects to consume, `apt install libopencl-icd-dev` will only get us as far as users occasionally having 2 year old dependencies. )_

Start by reading the linked OpenGL, OpenCL-on-Linux, Vulkan, and OpenCL-Primer guides, then clarify the intended platforms and scope with the maintainers. Done means an agreed Markdown Getting Started Guide covering the selected setup, compilation, IDE, and package-manager guidance.

Written by the indexing model from the issue text.