clarify IOCCC subject line requirements

contact.html

@@ -515,6 +515,7 @@ for more information on Mastodon.</p>
 <p>You <strong>MUST</strong> include the following two words (separated by a space) in the subject of your email, otherwise the email will be rejected:</p>
 <pre><code>    IOCCC YYYY</code></pre>
 <p><strong>IMPORTANT:</strong> The <em>YYYY</em> in the above email address <strong>MUST</strong> be changed to the current 4 digit year!</p>
+<p><strong>IMPORTANT:</strong> Do <strong>NOT</strong> immediately proceed nor follow the two words with punctuation. For example, neither <code>IOCCC 2025.</code> <strong>NOR</strong> <code>Re:IOCCC 2025</code> will work in the subject line because there are non-whitespace characters next to the 2 words! Instead use <code>IOCCC 2025 question.</code> or <code>Re: IOCCC 2025</code> or just <code>IOCCC 2025</code> on the subject line.</p>
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