title: R notebook font size
body: <p>What are my options for changing the font size of dynamically-generated output, when rendering to a PDF?  My document currently looks something like this:</p>
  
  <pre><code>---
  title: "Foo"
  author: "Bar"
  date: "`r format(Sys.time(), '%B %e, %Y')`"
  output:
    pdf_document: default
    html_document:
      df_print: paged
  header-includes: \usepackage{amsmath} \usepackage{color}
  ---
  
  # Introduction
  
  ```{bash echo=FALSE}
  perl -le 'print for 1..50'
  ```
  </code></pre>
  
  <p>I want to decrease the font size to help more output fit on a single page of the PDF.  I'm not currently also outputting to HTML, so a cross-format solution would be cool but not really necessary.</p>