title: How to print RMarkdown code chunk execution times?
body: <p>Just wondering if there's a way to capture (and print) execution time for code chunks in an Rmarkdown document (without wrapping every chunk in <code>system.time()</code>).</p>
  
  <p>Ideally I'd like to print an execution time underneath selected code chunks, but I would also be happy with just a summary table showing execution times at the end of the document.</p>
  
  <p>Thx.</p>