Updates to 2020/ferguson2

Added testing procedure (markdown, html: testing-procedure.{md,html}).
Updated the recode.{md,html} and README.md for this as well.

Updated the hidden message file (enigma.html) for a bit more fun.

Updated manifest, rebuilt index.html and .entry.json.

2020/ferguson2/recode.html

@@ -877,8 +877,11 @@ think that I would give too much away? :)</p>
 the key you wish to select is</p>
 <pre><code>    0EZ4PC1CC0PGTAQSOXWNMDRYKFUZEI</code></pre>
 <p>you can do:</p>
-<pre><code>    ./recode -R0EZ4PC1CC0PGTAQSOXWNMDRYKFUZEI -fenigma.html | ./prog - 2&gt;/dev/null &gt; decrypted.html</code></pre>
-<p>Then open <code>decrypted.html</code> in your browser.</p>
+<pre><code>    ./recode -R0EZ4PC1CC0PGTAQSOXWNMDRYKFUZEI -fenigma.html | ./prog - 2&gt;/dev/null &gt; enigma.deciphered.html</code></pre>
+<p>Then open <code>enigma.deciphered.html</code> in your browser. A command is provided in
+<a href="testing-procedure.html">testing-procedure.html</a> that does this too but it
+shows how you can use a file as input for the key instead as well as how I
+tested the code.</p>
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