Add note about quality of slides

index.html

@@ -78,7 +78,7 @@
         <em class="sidenote">(<a href="#jureca_jupyter">see below</a> for JURECA Jupyter task bundle)</em></li>
       <li>Slides
         <ul>
-          <li><a href="Introduction-to-Pandas--slides.pdf">PDF</a></li>
+          <li><a href="Introduction-to-Pandas--slides.pdf">PDF</a> (exported from HTML presentation; imperfect)</li>
           <li><a href="Introduction-to-Pandas--slides.ipynb">Jupyter Notebook</a></li>
           <li><a href="pandas-tutorial-slides.tar.gz">HTML presentation bundle</a></li>
         </ul>