Adds docs to generic_alert.md

doc/user/project/integrations/generic_alerts.md

+# Generic alerts integration **(ULTIMATE)**
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab-ee/issues/13203) in [GitLab Ultimate](https://about.gitlab.com/pricing/) 12.3.
+
+GitLab can accept alerts from any source via a generic webhook receiver.
+When you set up the generic alerts integration, a unique endpoint will
+be created which can receive a payload in JSON format, and will in turn
+create an issue with the payload in the body of the issue. You can always
+[customize the payload](#customizing-the-payload) to your liking.
+
+The entire payload will be posted in the issue discussion as a comment
+authored by the GitLab Alert Bot.
+
+## Setting up generic alerts
+
+To set up the generic alerts integration:  
+
+1. Navigate to **Settings > Integrations** in a project.  
+1. Click on **Alert endpoint**.
+1. Toggle the **Active**  alert setting. The `URL` and `Authorization Key` for the webhook configuration can be found there.  
+
+## Customizing the payload
+
+You can customize the payload by sending the following parameters. All fields are optional:
+
+| Property | Type | Description |
+| -------- | ---- | ----------- |
+| `title` | String | The title of the incident. If none is provided, then `New: Incident #N` will be used, where `#N` is the number of incident |
+| `description` | String | A high-level summary of the problem. |
+| `start_time` | DateTime | The time of the incident. If none is provided, a timestamp of the issue will be used. |
+| `service` | String | The affected service. |
+| `monitoring_tool` | String |  The name of the associated monitoring tool. |
+| `hosts` | String or Array | One or more hosts, as to where this incident ocurred. |
+
+Example request:
+
+```sh
+curl --request POST --data '{"title": "Incident title"}' --header "Authorization: Bearer <autorization_key>" <url>
+```
+
+The `<autorization_key>` and `<url>` values can be found when [setting up generic alerts](#setting-up-generic-alerts).
+
+Example payload:
+
+```json
+{
+  "title": "Incident title",
+  "description": "Short description of the incident",
+  "start_time": "2019-09-12T06:00:55Z",
+  "service": "service affected",
+  "monitoring_tool": "value",
+  "hosts": "value",
+}
+```

doc/user/project/integrations/project_services.md

@@ -34,6 +34,7 @@ Click on the service links to see further configuration instructions and details
 | [Emails on push](emails_on_push.md) | Email the commits and diff of each push to a list of recipients |
 | External Wiki | Replaces the link to the internal wiki with a link to an external wiki |
 | Flowdock | Flowdock is a collaboration web app for technical teams |
+| [Generic alerts](generic_alerts.md) **(ULTIMATE)** | Receive alerts on GitLab from any source |
 | [GitHub](github.md) **(PREMIUM)** | Sends pipeline notifications to GitHub |
 | [Hangouts Chat](hangouts_chat.md) | Receive events notifications in Google Hangouts Chat |
 | [HipChat](hipchat.md) | Private group chat and IM |