add detail about placing index.Rmd in a root project for rendering

[ryanpeek]

If getting "no input RMarkdown found from current directory error..." when trying to render, need to:

a) Put everything into an RStudio project (name whatever is best for you). Put all files that were created into the new project dir (or create a project and then create from aggiedown template). Then should be able to render since it's looking in the root directory. b) Set working directory for where the index.Rmd file lives (setwd()). Not ideal, but functional.