feat: add to top button as an option

assets/js/to-top.js

@@ -0,0 +1,20 @@
+var topbutton = document.getElementById('toTop');
+
+if (topbutton !== null) {
+
+  topbutton.style.display = 'none';
+  window.onscroll = function() {
+    scrollFunction()
+  };
+
+}
+
+function scrollFunction() {
+
+  if (document.body.scrollTop > 40 || document.documentElement.scrollTop > 40) {
+    topbutton.style.display = 'block';
+  } else {
+    topbutton.style.display = 'none';
+  }
+
+}