title: Best way to render a single Rmd file using blogdown
body: <p>We have a set of Rmd reports that live in a "knowledge repository" that we render via blogdown.</p>
  
  <p>We'd like to facilitate someone rendering a single report. Is there a best way to do this using blogdown? </p>
  
  <p>If not, what about adding a <code>files</code> argument to <code>render</code>, such that the specified files are rendered (and if not specified, defaults to the current behavior)?</p>