chore: add og:image to index.html

Author: remarkablemark

index.html

@@ -8,7 +8,11 @@
     />
     <meta name="viewport" content="width=device-width, initial-scale=1" />
     <meta name="theme-color" content="#000000" />
-    <meta name="description" content="Rhythmism is a web rhythm game." />
+    <meta name="description" content="🎶 Rhythmism is a web rhythm game." />
+    <meta
+      property="og:image"
+      content="https://remarkablegames.org/rhythmism/musical-note.png"
+    />
 
     <!--
       manifest.json provides metadata used when your web app is installed on a