title: Markdown files (names): is "index.md" - mandatory?
body: <p>It's obviously popular at least, but MUST the "main" file in a mkdocs directory be called index.md?   What if I reference documents in a file folder that is elsewhere, ie not part of this file's heirarchy?  I ask as I'm having a slight issue with files linked that are elsewhere.  There is little if any documentation about this on the 'net that I have found.  Thx</p>