Adds test counter to footer.

src/components/Footer.astro

@@ -4,6 +4,10 @@ const today = new Date();
 
 <footer>
 	&copy; {today.getFullYear()} Periodic. All rights reserved.
+  <script
+    data-goatcounter="https://goatcounter.terakoda.com/count"
+    async
+    src="https://www.terakoda.com/count.js"></script>
 </footer>
 <style>
 	footer {