docs: add showcase section to the contributing guide (#1606)

Co-authored-by: Sarah Rainsberger <5098874+sarah11918@users.noreply.github.com>
Co-authored-by: Elian <15145918+ElianCodes@users.noreply.github.com>
Co-authored-by: casungo <25723446+casungo@users.noreply.github.com>
Co-authored-by: Atharva <88548999+at-the-vr@users.noreply.github.com>

CONTRIBUTING.md

@@ -254,3 +254,28 @@ To add a language, you will need its BCP-47 tag and a label. See [“Adding a ne
 [gfi]: https://github.com/withastro/starlight/issues?q=is%3Aissue+is%3Aopen+label%3A%22good+first+issue%22+
 [api-docs]: https://docs.astro.build/en/reference/integrations-reference/
 [vitest]: https://vitest.dev/
+
+## Showcase
+
+We love to see websites built with Starlight and share them with the community on our [showcase](https://starlight.astro.build/resources/showcase/) page.
+If you’ve built a documentation site with Starlight, adding it to the showcase is just a pull request away!
+
+1. Set up a development environment by following the [“Setting up a development environment”](#setting-up-a-development-environment) instructions.
+2. Add a screenshot of your site to the `docs/src/assets/showcase/` directory. The image file must:
+   - Be a `.png` file and named after your site’s domain, e.g. `example.com.png`.
+   - Have the dimensions of 800 × 450 pixels.
+3. Add a new entry for your website in `docs/src/components/showcase-sites.astro`.
+
+   - The new entry must be appended at the end of the existing list of sites.
+   - The `title` attribute must be the name of your site with no extra details.
+   - The `href` attribute must be the URL of your Starlight site. If your documentation is hosted on a subdomain or subdirectory, include that in the URL.
+   - The `thumbnail` attribute must be the filename of the screenshot you added in step 2.
+
+   ```diff
+     <Card title="Example" href="https://example.com" thumbnail="example.com.png" />
+     <Card title="Last Example" href="https://example.org" thumbnail="example.org.png" />
+   + <Card title="Example" href="https://example.com" thumbnail="example.com.png" />
+   </FluidGrid>
+   ```
+
+4. Open a pull request on GitHub to add your changes.

docs/src/content/docs/resources/showcase.mdx

@@ -7,7 +7,7 @@ sidebar:
 
 :::tip[Add your own!]
 Have you built a Starlight site?
-Open a PR adding a link to this page!
+[Open a PR](https://github.com/withastro/starlight/blob/main/CONTRIBUTING.md#showcase) adding a link to this page!
 :::
 
 ## Sites