Update index.html

update option : --pdf to --output-diff

index.html

@@ -36,10 +36,10 @@ <h2 id="project_tagline">A simple tool for visually comparing two PDF files</h2>
 
 <p>It takes two PDF files as arguments. By default, its only output is its return
 code, which is 0 if there are no differences and 1 if the two PDFs differ. If
-given the <code>--pdf</code> option, <em>diff-pdf</em> produces a PDF file with
+given the <code>--pdf</code> option, <em>output-diff</em> produces a PDF file with
 visually highlighted differences:</p>
 
-<pre><code>$ diff-pdf --pdf=diff.pdf a.pdf b.pdf
+<pre><code>$ diff-pdf --output-diff=diff.pdf a.pdf b.pdf
 </code></pre>
 
 <p>Another option is to compare the two files visually in a simple GUI, using