**docs(readme): fix demo link and update GitHub Actions workflow versions**

### Changes:
- **README.md**: Corrected the relative path for the live demo link to `examples/demo.html`.
- **github-pages.yml**:
  - Updated GitHub Actions steps to their latest versions:
    - `actions/checkout@v4`
    - `actions/configure-pages@v4`
    - `actions/upload-pages-artifact@v3`
    - `actions/deploy-pages@v4`
  - Ensured compatibility with the latest versions of the workflow actions.

### Purpose:
Fixed a broken link in the README for better user accessibility to the demo. Updated workflow actions in `github-pages.yml` to leverage the latest performances and features.

.github/workflows/github-pages.yml

@@ -18,16 +18,16 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
-      
+        uses: actions/checkout@v4
+
       - name: Setup Pages
-        uses: actions/configure-pages@v3
-      
+        uses: actions/configure-pages@v4
+
       - name: Upload artifact
-        uses: actions/upload-pages-artifact@v2
+        uses: actions/upload-pages-artifact@v3
         with:
           path: './examples'  # Upload the examples directory
-      
+
       - name: Deploy to GitHub Pages
         id: deployment
-        uses: actions/deploy-pages@v2
+        uses: actions/deploy-pages@v4

README.md

@@ -955,7 +955,7 @@ Before deploying, make sure to configure the appropriate environment variables i
 The repository includes a comprehensive demo that showcases Brainy's main features:
 
 - `examples/demo.html` - A single demo page with animations demonstrating Brainy's features. 
-  - **[Try the live demo](https://soulcraft.github.io/brainy/demo.html)** - Check out the interactive demo on GitHub Pages
+  - **[Try the live demo](https://soulcraft.github.io/brainy/examples/demo.html)** - Check out the interactive demo on GitHub Pages
   - Or run it locally with `npm run demo` (see [demo instructions](README.demo.md) for details)
 
 The demo showcases: