add a consistent set of text about X11

1992/kivinen/README.md

@@ -6,6 +6,11 @@ If your machine support the X Window System, Version 11:
     make alt
 ```
 
+NOTE: this entry requires the `X11/Xlib.h` header file and the X11 library to
+compile.  See the
+FAQ on "[X11](../../faq.html#X11)"
+if you need help.
+
 We recommend that you try the alt version first so you can get a better idea of
 what this looked like back in 1992. See [original code](#original-code) for the
 original should you wish to see what we mean.

1992/kivinen/index.html

@@ -410,6 +410,10 @@ Location: <a href="../../location.html#FI">FI</a> - <em>Republic of Finland </em
 <h2 id="to-build">To build:</h2>
 <p>If your machine support the X Window System, Version 11:</p>
 <pre><code>    make alt</code></pre>
+<p>NOTE: this entry requires the <code>X11/Xlib.h</code> header file and the X11 library to
+compile. See the
+FAQ on “<a href="../../faq.html#X11">X11</a>”
+if you need help.</p>
 <p>We recommend that you try the alt version first so you can get a better idea of
 what this looked like back in 1992. See <a href="#original-code">original code</a> for the
 original should you wish to see what we mean.</p>