Update favicon and OpenGraph images (#5244)

Borrowed these from the reactjs/reactjs.org repo on GitHub:

- https://github.com/reactjs/reactjs.org/blob/master/static/logo-og.png
- https://github.com/reactjs/reactjs.org/blob/master/static/favicon.ico

website/siteConfig.js

@@ -34,7 +34,7 @@ const siteConfig = {
   /* path to images for header/footer */
   headerIcon: 'img/docusaurus.svg',
   footerIcon: 'img/docusaurus.svg',
-  favicon: 'img/favicon.png',
+  favicon: 'img/favicon/favicon.ico',
 
   /* Colors for website */
   colors: {
@@ -73,8 +73,8 @@ const siteConfig = {
   cleanUrl: true,
 
   // Open Graph and Twitter card images.
-  ogImage: 'img/docusaurus.png',
-  twitterImage: 'img/docusaurus.png',
+  ogImage: 'img/logo-og.png',
+  twitterImage: 'img/logo-og.png',
 
   // You may provide arbitrary config keys to be used as needed by your
   // template. For example, if you need your repo's URL...