chore: add contributing file

Author: Kumzy

CONTRIBUTING.md

@@ -0,0 +1,45 @@
+# Contribution guide
+
+> This guide applies to **litestar.dev** — the marketing and community website
+> for the Litestar framework. To contribute to the framework itself, see
+> [`litestar-org/litestar/CONTRIBUTING.rst`](https://github.com/litestar-org/litestar/blob/main/CONTRIBUTING.rst).
+
+## Setup
+
+1. Install [Node.js 24](https://nodejs.org/).
+2. Enable Corepack so the pinned `pnpm` version is used: `corepack enable`.
+3. Install dependencies: `pnpm install`.
+
+## Workflow
+
+1. Fork and clone the repo, then create a branch.
+2. `pnpm dev` — dev server at http://localhost:3000.
+3. `pnpm format && pnpm lint && pnpm test-all` before pushing (mirrors CI).
+4. Open a PR with a descriptive title referencing any related issue.
+
+## Tests
+
+| Project | Command           | Purpose                                                       |
+| ------- | ----------------- | ------------------------------------------------------------- |
+| `unit`  | `pnpm test-unit`  | Pure-function tests (helpers, composables)                    |
+| `nuxt`  | `pnpm test-nuxt`  | Tests needing the Nuxt runtime                                |
+| `build` | `pnpm test-build` | Post-build smoke tests — run **after** `pnpm generate-github` |
+
+`pnpm test-all` runs `unit` + `nuxt`.
+
+## Content
+
+Drop a Markdown / YAML file in the right place — `nuxt generate` picks it up.
+
+| Add                | Where                                            |
+| ------------------ | ------------------------------------------------ |
+| Blog post          | `content/blog/`                                  |
+| Sponsor            | `content/sponsors/`                              |
+| Starter / template | `content/starters/` or `content/templates/`      |
+| Page copy          | `content/*.yml` (schemas in `content.config.ts`) |
+
+## UI changes
+
+For anything visual, run `pnpm dev` and check dark mode + mobile width. Run
+`pnpm generate-github` to catch SSR / prerender / OG-image errors that only
+appear at build time.

README.md

@@ -33,9 +33,9 @@ The site is automatically deployed to GitHub Pages via GitHub Actions when chang
 pnpm generate
 ```
 
-## Testing
+## Contributing
 
-TODO
+See [CONTRIBUTING.md](./CONTRIBUTING.md) for setup, workflow, tests, and how to add content.
 
 ## Inspiration