add a consistent set of text about X11

2004/vik1/index.html

@@ -409,6 +409,9 @@ Location: <a href="../../location.html#US">US</a> - <em>United States of America
 <!-- BEFORE: 1st line of markdown file: 2004/vik1/README.md -->
 <h2 id="to-build">To build:</h2>
 <pre><code>    make</code></pre>
+<p>NOTE: this entry requires the <code>X11/Xlib.h</code> header file and the X11 library to
+compile. For more information see the
+FAQ on “<a href="../../faq.html#X11">X11</a>”.</p>
 <h2 id="to-use">To use:</h2>
 <pre><code>    ./vik1 [arg]</code></pre>
 <h2 id="try">Try:</h2>