docs(CONTRIBUTING): e2e how to

CONTRIBUTING.md

@@ -60,18 +60,40 @@ Point your browser to http://localhost:3000 :tada:
 
 ### Testing and Linting
 
-To only run linting:
+#### Run linting
 
 ```sh
 npm run lint
 ```
 
-To only run tests:
+#### Run unit tests
 
 ```sh
 npm run test
 ```
 
+#### Run e2e
+
+```sh
+npm run test:e2e
+```
+
+NB: dev server must be stopped.
+
+#### Run e2e with Cypress UI and watch mode
+
+In one terminal tab start environment:
+
+```sh
+npm run test:e2e
+```
+
+In another:
+
+```sh
+cypress open
+```
+
 ### Docs
 
 Improvements to the documentation are always welcome. You can find them in the [`docs`](/docs) path.