added a note aboit the "synchronize options" input

extension/ui/pages/help.html

@@ -399,6 +399,10 @@
 				</ul>
 				<p>Form buttons</p>
 				<ul>
+					<li><span class="option">synchronize options</span>
+						<p>Check this option to synchronize your options with the account associated to
+							your browser session.</p>
+					</li>
 					<li><span class="option">Reset</span>
 						<p>Reset all options to their default values.</p>
 					</li>