feat: add canonical url

excalidraw-app/index.html

@@ -54,6 +54,8 @@
       content="https://excalidraw.com/og-image-3.png"
     />
 
+    <link rel="canonical" href="https://excalidraw.com" />
+
     <!------------------------------------------------------------------------->
     <!--   to minimize white flash on load when user has dark mode enabled   -->
     <script>