Add id for signatories section

Author: marcprux

src/pages/open-letter.astro

@@ -30,7 +30,7 @@ function logoPath(url: string): string {
 <Letter {...data}>
   <article class="prose dark:prose-invert">
     <Content />
-    <div class="signatories">
+    <div class="signatories" id="signatories">
       <div class="sig-rule"></div>
       <h2>Signatories</h2>
       <ol>