Docs: Setting up two-column layout on docs homepage

To provide a better user experience, I’d like to set up a two-column layout on the main LLVM docs page. I’ve done some research and it looks like the way to do this is to use the raw directive to add html to the .rst source file.

Per the docutils documentation, “The use of “raw” ties documents to specific output formats and makes them less portable.”

I don’t think this should be a problem as I’m pretty sure that the LLVM docs are only served up as HTML. If I’m mistaken or if anyone has any objections, please let me know. Thanks!