Document how to consume the shared formatting baseline.

Explain the new Prettier baseline, recommended adoption steps, and editor alignment so downstream repositories can import and apply the config consistently.

Author: benzekrimaha

README.md

@@ -8,3 +8,63 @@ This project:
 * Provides an `eslint-config-scality` package that can be added as a dependency
   in other projects. That way, coding style can automatically be checked using
   eslint.
+
+## Prettier baseline
+
+This repository also provides a **baseline Prettier configuration** for Scality
+object repositories: 4-space JavaScript/TypeScript indentation, 120-character
+line length, single quotes, semicolons, trailing commas, and
+`quoteProps: 'as-needed'`.
+
+The configuration lives in `prettier.config.cjs`.
+
+To use it in a project:
+
+1. Install Prettier in the project:
+
+   ```sh
+   yarn add --dev prettier
+   # or
+   npm install --save-dev prettier
+   ```
+
+2. Copy or extend the configuration:
+
+   ```js
+   // prettier.config.cjs
+   module.exports = require('eslint-config-scality/prettier.config.cjs');
+   ```
+
+3. Add convenience scripts:
+
+   ```json
+   {
+     "scripts": {
+       "format": "prettier --write .",
+       "format:check": "prettier --check ."
+     }
+   }
+   ```
+
+Projects are free to override options locally (for example `tabWidth` or
+`printWidth`) if they have strong legacy constraints, but this configuration
+is intended to be the **default Scality baseline** for new or reformatted
+Node.js codebases. YAML defaults to 2-space indentation, JSON and Markdown to
+4-space indentation, and Markdown prose is left un-reflowed by default
+(`proseWrap: 'preserve'`) to avoid noisy diffs in existing documentation.
+
+## Editor configuration
+
+For a consistent editor experience, you can copy or adapt the `.editorconfig`
+from this repository. It aligns with the ESLint and Prettier baselines:
+
+- **JS/TS**: spaces with 4-space indentation.
+- **JSON/Markdown**: spaces with 4-space indentation.
+- **YAML**: spaces with 2-space indentation.
+- `end_of_line = lf`, `insert_final_newline = true`,
+  `trim_trailing_whitespace = true`.
+
+## Contributing
+
+- See `CONTRIBUTING.md` for contribution guidelines and coding standards.
+- See `TESTING.md` for details on running the linters and tests in this repo.