Added the Fortigate component documentation (#9807)

* Added the Fortigate component documentation

* Update source/_components/fortigate.markdown

Co-Authored-By: Franck Nijhof <frenck@frenck.nl>

* Update source/_components/fortigate.markdown

Co-Authored-By: Franck Nijhof <frenck@frenck.nl>

* Update source/_components/fortigate.markdown

Co-Authored-By: Franck Nijhof <frenck@frenck.nl>

* Update source/_components/fortigate.markdown

Co-Authored-By: Franck Nijhof <frenck@frenck.nl>

* Update source/_components/fortigate.markdown

Co-Authored-By: Klaas Schoute <klaas_schoute@hotmail.com>

* Update source/_components/fortigate.markdown

Co-Authored-By: Klaas Schoute <klaas_schoute@hotmail.com>

* Update source/_components/fortigate.markdown

Co-Authored-By: Klaas Schoute <klaas_schoute@hotmail.com>

* fixed some remaks

* rewording

* Move setup up

source/_components/fortigate.markdown

@@ -0,0 +1,81 @@
+---
+layout: page
+title: "Fortigate"
+description: "Instructions on how to integrate Fortigate Firewalls into Home Assistant."
+date: 2019-07-07 22:00
+sidebar: true
+comments: false
+sharing: true
+footer: true
+logo: fortinet.jpg
+ha_category:
+  - Presence Detection
+ha_release: 0.96
+ha_iot_class: Local Polling
+---
+
+This is a Fortigate presence sensor based on device detection of the Fortigate API
+
+## Fortigate setup
+
+Configure the Fortigate with a USERNAME API user and assign its minimum rights profile :
+
+```text
+config system accprofile
+    edit "homeassistant_profile"
+        set authgrp read
+    next
+end
+
+config system api-user
+    edit "USERNAME"
+        set api-key API_KEY
+        set accprofile "homeassistant_profile"
+        set vdom "root"
+        config trusthost
+            edit 1
+                set ipv4-trusthost <trusted subnets>
+            next
+        end
+    next
+end
+```
+
+## Configuration
+
+Add the following to your `configuration.yaml` file:
+
+```yaml
+# Example configuration.yaml entry
+fortigate:
+  host: HOST_IP
+  username: YPUR_USERNAME
+  api_key: YOUR_API_KEY
+```
+
+{% configuration %}
+host:
+  description: The IP address of the Fortigate device.
+  required: true
+  type: string
+username:
+  description: The username of the user that will connect to the Fortigate device.
+  required: true
+  type: string
+api_key:
+  description: The API key associated with the user.
+  required: true
+  type: string
+devices:
+  description: The MAC addresses of the devices to monitor.
+  required: false
+  type: string
+{% endconfiguration %}
+
+### Errors
+
+If the rights of the profile are not sufficient, you will get the following error:
+
+```txt
+ERROR (MainThread) [homeassistant.core] Error doing job: Task exception was never retrieved
+```