Surface the "what's new" section in more places.

[hayleigh-dot-dev]

We try to keep a running log of new developments in the library or our documentation, but currently it's somewhat hidden under the "community" menu. This PR addresses that by adding two new things:

• A new section on the home page:

• A new section underneath the table of contents sidebar in our guides:

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Name	Status	Preview	Comments	Updated (UTC)
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| Name | Status | Preview | Comments | Updated (UTC) | | :--- | :----- | :------ | :------- | :------ | | **xyflow-svelte-examples** | ⬜️ Ignored ([Inspect](https://vercel.com/xyflow/xyflow-svelte-examples/HUyC7UhuCKd7C61zn3jgncMJJNsb)) | [Visit Preview](https://xyflow-svelte-examples-git-pitch-surface-whats-ne-8150c3-xyflow.vercel.app) | | Jun 4, 2024 2:18pm | | **xyflow-website** | ⬜️ Ignored ([Inspect](https://vercel.com/xyflow/xyflow-website/urRgE5ehYSXEj7sYjSQKpYk8JQnF)) | [Visit Preview](https://xyflow-website-git-pitch-surface-whats-new-section-xyflow.vercel.app) | | Jun 4, 2024 2:18pm |