Document the cutoff, since it's nontrivial now

docs/content/documentation/content/page.md

@@ -155,10 +155,18 @@ template = "page.html"
 You can ask Zola to create a summary if, for example, you only want to show the first
 paragraph of the page content in a list.
 
-To do so, add <code>&lt;!-- more --&gt;</code> in your content at the point
+To do so, add `<!-- more -->` in your content at the point
 where you want the summary to end. The content up to that point will be
 available separately in the
 [template](@/documentation/templates/pages-sections.md#page-variables) via `page.summary`.
 
 A span element in this position with a `continue-reading` id is created, so you can link directly to it if needed. For example:
 `<a href="{{ page.permalink }}#continue-reading">Continue Reading</a>`.
+
+If the `<!-- more -->` marker exists in the middle of a line, the summary will contain a span with a `summary-cutoff` class so you can configure the way the cutoff is rendered. For example, this CSS will display it as an ellipsis:
+
+```css
+.summary-cutoff::before {
+    content: "\2027";
+}
+```