Add content to index.rst

I created a folder called Read The Docs, where I am adding a Read The Docs building file called index.rst, and all its dependencies, where we will keep Cling-related documentation that it is not for developers.

I added a link to Cling's GitHub webpage for download, last release, etc. I added a link to the Compiler Research Webpage.

I am comparing two styles: References listed as text lines, or organized in a table.