Added Prepr CMS Examples to docs (vercel#23221)

Following commit vercel@1f5c2c8

Adding documentation links to example.

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [X ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.

## Documentation / Examples

- [x ] Make sure the linting passes

Author: tim-hanssen

Diff for: docs/advanced-features/preview-mode.md

@@ -16,6 +16,7 @@ description: Next.js has the preview mode for statically generated pages. You ca
     <li><a href="https://github.com/vercel/next.js/tree/canary/examples/cms-prismic">Prismic Example</a> (<a href="https://next-blog-prismic.now.sh/">Demo</a>)</li>
     <li><a href="https://github.com/vercel/next.js/tree/canary/examples/cms-contentful">Contentful Example</a> (<a href="https://next-blog-contentful.now.sh/">Demo</a>)</li>
     <li><a href="https://github.com/vercel/next.js/tree/canary/examples/cms-strapi">Strapi Example</a> (<a href="https://next-blog-strapi.now.sh/">Demo</a>)</li>
+    <li><a href="https://github.com/vercel/next.js/tree/canary/examples/cms-prepr">Prepr Example</a> (<a href="https://next-blog-prepr.now.sh/">Demo</a>)</li>    
     <li><a href="https://github.com/vercel/next.js/tree/canary/examples/cms-agilitycms">Agility CMS Example</a> (<a href="https://next-blog-agilitycms.now.sh/">Demo</a>)</li>
     <li><a href="https://github.com/vercel/next.js/tree/canary/examples/cms-cosmic">Cosmic Example</a> (<a href="https://next-blog-cosmic.now.sh/">Demo</a>)</li>
     <li><a href="https://github.com/vercel/next.js/tree/canary/examples/cms-buttercms">ButterCMS Example</a> (<a href="https://next-blog-buttercms.now.sh/">Demo</a>)</li>

Diff for: docs/basic-features/data-fetching.md

@@ -17,6 +17,7 @@ description: 'Next.js has 2 pre-rendering modes: Static Generation and Server-si
     <li><a href="https://github.com/vercel/next.js/tree/canary/examples/cms-prismic">Prismic Example</a> (<a href="https://next-blog-prismic.now.sh/">Demo</a>)</li>
     <li><a href="https://github.com/vercel/next.js/tree/canary/examples/cms-contentful">Contentful Example</a> (<a href="https://next-blog-contentful.now.sh/">Demo</a>)</li>
     <li><a href="https://github.com/vercel/next.js/tree/canary/examples/cms-strapi">Strapi Example</a> (<a href="https://next-blog-strapi.now.sh/">Demo</a>)</li>
+    <li><a href="https://github.com/vercel/next.js/tree/canary/examples/cms-prepr">Prepr Example</a> (<a href="https://next-blog-prepr.now.sh/">Demo</a>)</li>
     <li><a href="https://github.com/vercel/next.js/tree/canary/examples/cms-agilitycms">Agility CMS Example</a> (<a href="https://next-blog-agilitycms.now.sh/">Demo</a>)</li>
     <li><a href="https://github.com/vercel/next.js/tree/canary/examples/cms-cosmic">Cosmic Example</a> (<a href="https://next-blog-cosmic.now.sh/">Demo</a>)</li>
     <li><a href="https://github.com/vercel/next.js/tree/canary/examples/cms-buttercms">ButterCMS Example</a> (<a href="https://next-blog-buttercms.now.sh/">Demo</a>)</li>

Diff for: docs/basic-features/pages.md

@@ -56,6 +56,7 @@ You can also use **Client-side Rendering** along with Static Generation or Serve
     <li><a href="https://github.com/vercel/next.js/tree/canary/examples/cms-prismic">Prismic Example</a> (<a href="https://next-blog-prismic.now.sh/">Demo</a>)</li>
     <li><a href="https://github.com/vercel/next.js/tree/canary/examples/cms-contentful">Contentful Example</a> (<a href="https://next-blog-contentful.now.sh/">Demo</a>)</li>
     <li><a href="https://github.com/vercel/next.js/tree/canary/examples/cms-strapi">Strapi Example</a> (<a href="https://next-blog-strapi.now.sh/">Demo</a>)</li>
+    <li><a href="https://github.com/vercel/next.js/tree/canary/examples/cms-prepr">Prepr Example</a> (<a href="https://next-blog-prepr.now.sh/">Demo</a>)</li>    
     <li><a href="https://github.com/vercel/next.js/tree/canary/examples/cms-agilitycms">Agility CMS Example</a> (<a href="https://next-blog-agilitycms.now.sh/">Demo</a>)</li>
     <li><a href="https://github.com/vercel/next.js/tree/canary/examples/cms-cosmic">Cosmic Example</a> (<a href="https://next-blog-cosmic.now.sh/">Demo</a>)</li>
     <li><a href="https://github.com/vercel/next.js/tree/canary/examples/cms-buttercms">ButterCMS Example</a> (<a href="https://next-blog-buttercms.now.sh/">Demo</a>)</li>