docs: social previews (#730)

## 📜 Description

Enabled favicon in google search and static preview.

## 💡 Motivation and Context

I want `keyboard-controller` to be more recognizable.

## 📢 Changelog

<!-- High level overview of important changes -->
<!-- For example: fixed status bar manipulation; added new types
declarations; -->
<!-- If your changes don't affect one of platform/language below - then
remove this platform/language -->

### Docs

- added og preview (main webpage instead of empty);
- try to move `favicon.ico` to top level of access (so that it can be
indexed by google and show up in search results).

## 🤔 How Has This Been Tested?

Tested manually on localhost:3000

## 📝 Checklist

- [x] CI successfully passed
- [x] I added new mocks and corresponding unit-tests if library API was
changed

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

docs/docusaurus.config.js

@@ -19,7 +19,7 @@ const config = {
   baseUrl: baseUrl,
   onBrokenLinks: "throw",
   onBrokenMarkdownLinks: "warn",
-  favicon: "img/favicon.ico",
+  favicon: "favicon.ico",
 
   // GitHub pages deployment config.
   // If you aren't using GitHub pages, you don't need these.
@@ -105,6 +105,11 @@ const config = {
   themeConfig:
     /** @type {import('@docusaurus/preset-classic').ThemeConfig} */
     ({
+      image: "img/og-image.png",
+      metadata: [
+        { name: "og:image:width", content: "2400" },
+        { name: "og:image:height", content: "1426" },
+      ],
       navbar: {
         title: "Keyboard Controller",
         logo: {