Restore the missing overview documents to the CF home page

I have created a directory Data/cf-documents/overview/ and put the talk and the article in it. I believe these are the PDFs we had on the old CF website. They are both ten years old, but since none of the fundamentals have changed they're probably still useful. I have modified index.md to point to them. However, I am not sure if I've got this right, since I haven't found out how to test it in my forked repository. (This is the first time I've used git.) When I view index.md in firefox, blob/master is inserted in the URLs, not just of my files, but of the others with relative paths such as the FAQ. That's not where they are so the links are broken. Yet the main CF page does not have blob/master in the URLs. I don't understand this but I'm sure you do!