dashboard: mention the Chromium timer throttling issue

dashboard/dashboard.html

@@ -423,6 +423,9 @@
 			<p>
 				If your adblocker is enabled for this domain, you will see slower performance, and some URLs will not be displayed.
 			</p>
+			<p>
+				Chromium-based browser users (e.g. Chrome, Brave, Edge) may observe very long hangs when returning to this dashboard tab after leaving it in the background.  Run the browser with command-line argument <code>--disable-background-timer-throttling</code> to fix this issue.
+			</p>
 			<p>
 				A custom context menu is shown when right-clicking URLs in the log windows below.  It can be disabled by adding <kbd><span class="url-q-or-amp">?</span>contextMenu=0</kbd> to the dashboard URL.  Firefox users: if you see both the normal and custom context menu, make sure <code>dom.event.contextmenu.enabled</code> is set to <code>true</code> in <code>about:config</code>.
 			</p>