add variable `{save-action}`

src/ui/pages/help.html

@@ -928,6 +928,7 @@
 					<li><code>{profile-name}</code>: the name of the profile used to save the page</li>
 					<li><code>{filename-extension}</code>: the extension of the filename depending on the file format
 						(i.e. "html", "u.zip.html", "zip.html", "zip")</li>
+					<li><code>{save-action}</code>: the action used to save the page (i.e. "page", "selection")</li>
 				</ul>
 			</li>
 			<li><a id="template-functions" href="#template-functions">Template functions</a>