feat: use the first paragraph as the excerpt if description is not set

src/plugins/remark-excerpt.js

@@ -0,0 +1,16 @@
+import { toString } from 'mdast-util-to-string'
+
+/* Use the post's first paragraph as the excerpt */
+export function remarkExcerpt() {
+    return (tree, { data }) => {
+        let excerpt = '';
+        for (let node of tree.children) {
+            if (node.type !== 'paragraph') {
+                continue
+            }
+            excerpt = toString(node)
+            break
+        }
+        data.astro.frontmatter.excerpt = excerpt
+    };
+}