Fix some moments in documentation

doc/api/services.md

@@ -447,6 +447,8 @@ GET /projects/:id/services/gemnasium
 Google GSuite team collaboration tool.
+>**Note:** This service was [introduced in v11.2](https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/20290)
+
 ### Create/Edit Hangouts Chat service
 Set Hangouts Chat service for a project.

doc/user/project/integrations/hangouts_chat.md

@@ -9,11 +9,11 @@ The Hangouts Chat service sends notifications from GitLab to the room for which
 1. Click on **ADD WEBHOOK** and fill in the name of the bot that will post the messages. Optionally define avatar.
 1. Click **SAVE** and copy the **Webhook URL** of your webhook.
-Details: https://developers.google.com/hangouts/chat/how-tos/webhooks
+See also [the Hangouts Chat documentation for configuring incoming webhooks](https://developers.google.com/hangouts/chat/how-tos/webhooks)
 ## On GitLab
-When you have **Webhook URL** for your Hangouts Chat room webhook, you can setup the GitLab service.
+When you have the **Webhook URL** for your Hangouts Chat room webhook, you can setup the GitLab service.
 1. Navigate to the [Integrations page](project_services.md#accessing-the-project-services) in your project's settings, i.e. **Project > Settings > Integrations**.
 1. Select the **Hangouts Chat** project service to configure it.