add bottom of story chapter nav

css/index.scss

@@ -117,6 +117,10 @@ a:hover {
     overflow-wrap: anywhere;
 }
 
+.story-nav {
+    text-align: center;
+}
+
 .not-found-page {
     margin-top: 0.5em;
     display: flex;

src/routes/story.rs

@@ -54,6 +54,15 @@ pub async fn render(Query(params): Query<StoryParams>) -> Markup {
                                         })  { (PreEscaped(paragraph.html)) }
                                     }
                                 }
+                                div .story-nav {
+                                    @if part_idx > 0 {
+                                        a href=(format!("/story?id={}&chapter={}", story.id, part_idx-1)) { "<" }
+                                    }
+                                    " | "
+                                    @if part_idx < story._parts.len() - 1 {
+                                        a href=(format!("/story?id={}&chapter={}", story.id, part_idx+1)) { ">" }
+                                    }
+                                }
                             }
                         }
                     }