Add Suncel CMS (#828)

* Add Suncel CMS

* Add image

Author: Nicolas Rusig

src/site/headless-cms/suncel.md

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+---
+title: Suncel
+homepage: https://suncel.io/
+twitter: Suncel_io
+repo: suncel-io
+opensource: "No"
+typeofcms: "API Driven"
+supportedgenerators:
+  - Next.js
+description: Suncel is a headless CMS for Next.js, with a powerful no-code visual builder to rapidly create pages and publish your content.
+images:
+  - path: /img/cms/suncel-2.png
+  - path: /img/cms/suncel-1.png
+---
+
+## Quickstart
+
+Implement a CMS in your Next.js app with one npm package : `@suncel/nextjs`.
+
+- [Create an account](https://app.suncel.io/signup)
+- Install Suncel : check our [documentation](https://docs.suncel.io/developer/getting-started/manual-setup) use our CLI **npx create-suncel-app**, or go get our [starter project](https://github.com/suncel-io/suncel-nextjs-starter) for Next.js.
+
+## Benefits
+
+**For marketing team** : publish content 2x faster with a no-code editor. No complexity, focus on delivering content. Instant publish, don't wait for dev to publish your content.
+
+**For SEO** : SEO module, page optimization, better core web vitals, image optimization.
+
+**For developper** : installation in minutes, pre-built templates. Component-driven approach. Live preview when building a component.
+
+## Key features
+
+- Simple visual builder (no complexity)
+- SEO module
+- Multilanguage
+- Reusable components
+- Live preview in the builder
+- Pre-built templates
+- Basic components lib : richtext, images, links,...
+- Component variation
+- Admin and visual builder on your site
+- Pages and asset organized in folders
+- Self-hosted
+- Asset management / Media Library
+- User roles and permissions
+- Revision History