Rename this repo

[mmoult]

I would suggest renaming this repo to clarify its purpose, especially since shader-slang.github.io is redirected to shader-slang.com. I would propose slang-website (which I think matches the form established by slang-vscode-extension and slang-playground), but no need to choose that name if it is objectionable to you.

We may also want to consider that the address which hosts the website may change again, and it may be preferable to choose an abstracted repo name now to avoid multiple renames in the future.