Make ^NOTE in markdown/html files bold

2018/burton2/index.html

@@ -709,7 +709,7 @@ are not recognised when written as <code>-rs</code> in prose).</p>
     ./manpage.sh -h | ./manpage.sh
     ./manpage.sh -h | ./manpage.sh -R | less
     ./manpage.sh -h | ./manpage.sh -P | lpr</code></pre>
-<p>NOTE: in 2023 the <code>tac.man</code> was updated to proper man format and renamed
+<p><strong>NOTE</strong>: in 2023 the <code>tac.man</code> was updated to proper man format and renamed
 <a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2018/burton2/tac.1">tac.1</a>.</p>
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