Add readme file

README.md

+This module integrates to GitLab utilizing the GitLab API version 4.
+
+All API resources are available through simple calls like
+
+```php
+$this->api->getClient()->groups();
+```
+
+to receive a list of all groups on a GitLab instance.
+
+The module supports GitLab server profiles as config entities, so you can create
+as many you like and talk to all the GitLab instances that matter to you from
+within your Drupal site.
+
+This module also comes with a [webform](https://www.drupal.org/project/webform)
+handler plugin which allows you to create a new project from a webform
+submission.
+
+With the ECA GitLab API submodule, you can also leverage all API methods from
+within [ECA](https://www.drupal.org/project/eca) models.