Document CONSTANT VIGILANCE feature in help

src/options.html

@@ -69,6 +69,9 @@
 			<h3>Whitelist mode</h3>
 			<p>In <strong>whitelist mode</strong>, <em>the matching patterns list is ignored</em>. Stickies are <em>always</em> killed, <em>unless</em> the page matches one of the patterns in the <strong>exclusion patterns</strong> list.</p>
 			<p>(In whitelist mode, the behavior of the main button (<span class='fa fa-heavy'>&#xf08d;</span>) in the AlwaysKillSticky popup is reversed.)</p>
+			<h2>Constant vigilance</h2>
+			<p>Some websites add sticky elements after loading, or make existing elements sticky (either on a timer, or based on user actions). CONSTANT VIGILANCE 	counteracts this behavior, by watching the DOM for mutations, and, if	necessary, killing any newly-formed stickies.</p>
+			<p>This feature may slightly impact browser performance on some sites or some computers. If you disable it, stickies will still be killed immediately upon page load, but not thereafter.</p>
 			<h2>Advanced usage</h2>
 			<p>AlwaysKillSticky automatically manages the lists of matching and exclusion patterns. When you enable or disable sticky-killing for a site (by clicking the big button in the AlwaysKillSticky popup), the pattern lists are automatically modified appropriately. There is usually no need to edit the lists yourself.</p>
 			<p>However, if you prefer more fine-grained control (e.g., if you want to kill stickies on all sites on a domain, or if you want to exclude specific paths of a site), you can edit the pattern lists by hand. The matching and exclusion patterns are <a href='https://en.wikipedia.org/wiki/Regular_expression' rel='nofollow' target='_blank'>regular expressions</a> (a.k.a. “regexps”). (The site <a href='https://regexr.com/' rel='nofollow' target='_blank'>RegExr.com</a> is useful if you are not entirely familiar with how regexps work—or even if you are.)</p>