add a consistent set of text about X11

2011/toledo/README.md

@@ -1,11 +1,13 @@
 ## To build:
 
-If you have X11 installed:
-
 ``` <!---sh-->
     make
 ```
 
+NOTE: this entry requires the `X11/Xlib.h` header file and the X11 library to
+compile.  For more information see the
+FAQ on "[X11](../../faq.html#X11)".
+
 There are two alternate versions, [one that lets you reconfigure the
 controls and size](%%REPO_URL%%/2011/toledo/toledo.alt.c) and [another that should work for
 Windows](%%REPO_URL%%/2011/toledo/toledo.alt2.c). See [Alternate code](#alternate-code) below.

2011/toledo/index.html

@@ -408,8 +408,10 @@ Location: <a href="../../location.html#MX">MX</a> - <em>United Mexican States</e
 
 <!-- BEFORE: 1st line of markdown file: 2011/toledo/README.md -->
 <h2 id="to-build">To build:</h2>
-<p>If you have X11 installed:</p>
 <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>
 <p>There are two alternate versions, <a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2011/toledo/toledo.alt.c">one that lets you reconfigure the
 controls and size</a> and <a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2011/toledo/toledo.alt2.c">another that should work for
 Windows</a>. See <a href="#alternate-code">Alternate code</a> below.</p>