Add doc

Author: mclegrand

README.md

@@ -5,6 +5,21 @@ Repo containing code of:
 - [@gouvfr-lasuite/integration npm package](https://www.npmjs.com/package/@gouvfr-lasuite/integration) in [`packages/integration`](./packages/integration/)
 - [La Suite: integration docs and API](https://integration.lasuite.numerique.gouv.fr/) in [`website`](./website/)
 
+# Adapting to your needs
+
+This repository allows you to configure your version of La Gaufre. It contains a github action that will build it as a static website and host it on GitHub Pages, by default under `https://<yourname>.github.io/integration` once you fork it and enable Pages.
+
+You can configure La Gaufre by editing [website/src/data/services.json](website/src/data/services.json) (see file for DINUM default values) and adding the required logos with names `$id.svg` into [website/src/assets/logos/](website/src/assets/logos/).
+
+## Using La Gaufre
+
+In your application, add a `button` with the class `js-lasuite-gaufre-btn`, and include the js `https://<yourname>.github.io/integration/api/v1/gaufre.js` in a script element using id `lasuite-gaufre-script`. If necessary, you'll need to whitelist `https://<yourname>.github.io/` in relevant CORS and/or CSP. 
+
+If you are using the css from DINUM, you may also want to add classes `lasuite-gaufre-btn--vanilla js-lasuite-gaufre-btn` and either `lasuite-gaufre-btn--responsive`(responsive design) or `lasuite-gaufre-btn--small`(small design).
+
+Clicking the button should then load `https://<yourname>.github.io/integration/api/v1/gaufre/`.
+
+
 ## Licenses
 
 Source code is released under the [MIT](LICENSES/MIT.txt) and other