Post title: Add example of the block

[MaggieCabrera]

What?

Add a basic example to the core/post-title block.

Part of #30029

Why?

Because it was showing empty before

How?

I define a viewport size for the example

Testing Instructions

Open the block inserter and search for the title block, hover over it and you'll see the example

Testing Instructions for Keyboard

Screenshots or screencast

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

If you're merging code through a pull request on GitHub, copy and paste the following into the bottom of the merge commit message.

Co-authored-by: MaggieCabrera <[email protected]>
Co-authored-by: jameskoster <[email protected]>

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

[jameskoster]

Working for me :)