title: Adding system time and date to pdf with ggsave
body: <p>I have a pdf file that I trying to print with the time and date on the name of the pdf file. I tried using alot of different ways but still nothing. 
  Can you please help me with that? 
  The code for printing to pdf is below:</p>
  
  <pre><code>ggsave("Title of file.pdf", marrangeGrob(grobs = plots_list, nrow=1, ncol=1))
  </code></pre>