docs(cli-ui): add more notes for local development

packages/@vue/cli-ui/README.md

@@ -1,15 +1,38 @@
 # @vue/cli-ui
 
-Start development version:
+### Local development
+
+Before starting a local cli-ui instance,
+consider following the [contributing guide](https://github.com/vuejs/vue-cli/blob/dev/.github/CONTRIBUTING.md)
+in order to download all required dependencies of vue-cli's packages.
+
+Just after, you should build once then serve `@vue/cli-ui-addon-webpack` by running:
+```bash
+cd ../cli-ui-addon-webpack
+yarn build # just do once
+yarn serve
+```
+
+Then you start the ui server (based on Apollo):
+
+```
+cd ../cli-ui
+yarn run apollo
+```
+
+And then in another terminal, you should serve the ui web app:
 
 ```
 yarn run serve
 ```
 
-In another terminal:
+#### Testing
+
+For running E2E tests, you just need to run:
 
 ```
-yarn run apollo
+yarn run test:e2e
 ```
 
-You also need to build `@vue/cli-ui-addon-webpack`.
+This will open a new [Cypress](https://www.cypress.io/) window.
+You can now run all or specific integration tests.