Document Drupal Development Env: composer/plugin/drupal-development-environment#1

docs/composer/plugin/drupal-dev-environment/index.md

@@ -8,9 +8,20 @@ tags:
 ---
 # Drupal Development Environment
 
-This composer plugin builds all necessary structures of a Drupal project for development.
+In addition to the [Drupal Environment](../drupal-environment/index.md), this tool can be installed when
+developing Drupal modules, themes or styling pages. 
+This composer plugin builds all necessary infrastructure for a Drupal project to make development very handy.
+
+## Testing
+
 It provides a massive amount of testing tools, which can be executed out of the box using 
-[Ahoy](../../plugin/ahoy/index.md):
+[Ahoy](../../plugin/ahoy/index.md). To get an overview, just execute:
+
+```l3d
+a test --help
+```
+
+This will print out a list with all available tools:
 
 - [Dependency Analysis](../../../dev_tools/test.md#drupal-dependency-analysis)
 - [PHP Unit](../../../dev_tools/test.md#unitkernelfunctional-testing)
@@ -22,3 +33,14 @@ It provides a massive amount of testing tools, which can be executed out of the
 - [PHP Metrics](../../../dev_tools/test.md#php-metrics)
 - [Stylelint](../../../dev_tools/test.md#stylelint)
 - [Eslint](../../../dev_tools/test.md#es-lint)
+
+## Working with Themes
+
+The development plugin provides tools, that are common for working with themes in Drupal:
+
+- [Node.js](https://nodejs.org/)
+- [Gulp.js](https://gulpjs.com/)
+
+Now you can create or use existing `package.json` or `gulp.js` files for building your `css`, e.g.
+using [Sass](https://sass-lang.com/).
+