docs: ✏️ search (#1535)

added search with lunr

# Description

Please include a summary of the changes and the related issue. Please
also include relevant motivation and context.

## Checklist before requesting a review

Please delete options that are not relevant.

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented hard-to-understand areas
- [ ] I have ideally added tests that prove my fix is effective or that
my feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged

## Screenshots (if appropriate):

docs/docusaurus.config.js

@@ -31,6 +31,7 @@ const config = {
     defaultLocale: 'en',
     locales: ['en'],
   },
+  plugins: [require.resolve('docusaurus-lunr-search')],
 
   presets: [
     [

docs/package.json

@@ -18,6 +18,7 @@
     "@docusaurus/preset-classic": "2.4.1",
     "@mdx-js/react": "^1.6.22",
     "clsx": "^1.2.1",
+    "docusaurus-lunr-search": "^3.2.0",
     "prism-react-renderer": "^1.3.5",
     "react": "^17.0.2",
     "react-dom": "^17.0.2",