Update index.md, mkdocs.yml, add javascripts for correct translate

docs/javascripts/brand-notranslate.js

@@ -0,0 +1,14 @@
+// Keep the brand name "Bitcoin After Life" untranslated by Chrome / Google
+// Translate, while the rest of the page still translates normally.
+(function () {
+  function mark() {
+    document
+      .querySelectorAll('.md-header__topic .md-ellipsis, .bal-hero .name')
+      .forEach(function (el) {
+        el.setAttribute('translate', 'no');
+        el.classList.add('notranslate');
+      });
+  }
+  if (document.readyState !== 'loading') mark();
+  else document.addEventListener('DOMContentLoaded', mark);
+})();