docs: replace import of custom 'ListItem' component with inline html

[yakir-reznik]

🔗 Linked issue

#292 Similar to #232

❓ Type of change

• [x] 📖 Documentation (updates to the documentation, readme or JSdoc annotations)
• [x] 🐞 Bug fix (a non-breaking change that fixes an issue)
• [ ] 👌 Enhancement (improving an existing functionality like performance)
• [ ] ✨ New feature (a non-breaking change that adds functionality)
• [ ] 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• [ ] ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Resolves #292

The example code for the NavigationMenu contains an import of a custom component (ListItem).

This custom component will not be present on the user's project and will not be installed when the users installs the NavigationMenu component with the CLI (or by copy-pasting the code to their local project).

The import of the custom component causes the NavigationMenu to throw on when installed and used for the first time.

This error is also replicated when trying to run the example code in StackBlitz.

📸 Screenshots (if appropriate)

📝 Checklist

• [x] I have linked an issue or discussion.
• [x] I have updated the documentation accordingly.