Add documentation for Synology SRM device tracker (#8240)

* Add documentation for Synology SRM device tracker

* ✏️ Tweaks

source/_components/device_tracker.synology_srm.markdown

@@ -0,0 +1,67 @@
+---
+layout: page
+title: "Synology SRM"
+description: "Instructions on how to integrate Synology SRM routers into Home Assistant."
+date: 2019-01-22 13:43
+sidebar: true
+comments: false
+sharing: true
+footer: true
+logo: synology.png
+ha_category: Presence Detection
+ha_release: 0.87
+---
+
+This platform allows you to detect presence by looking at connected devices to a [Synology SRM](https://www.synology.com/en-us/srm) router.
+
+## {% linkable_title Configuration %}
+
+To use this device tracker in your installation, add the following to your `configuration.yaml` file:
+
+```yaml
+# Example configuration.yaml entry
+device_tracker:
+  - platform: synology_srm
+    host: 192.168.1.254
+    password: YOUR_ADMIN_PASSWORD
+```
+
+{% configuration %}
+host:
+  description: The Synology SRM router host or IP address, e.g., `192.168.1.1` or `router.mydomain.local`
+  required: true
+  type: string
+port:
+  description: The port to connect to the Synology SRM router.
+  required: false
+  default: 8001
+  type: int
+username:
+  description: The username of a user with administrative privileges.
+  required: false
+  default: admin
+  type: string
+password:
+  description: The password for your given admin account.
+  required: true
+  type: string
+ssl:
+  description: Use HTTPS instead of HTTP to connect.
+  required: false
+  default: true
+  type: boolean
+verify_ssl:
+  description: Enable or disable SSL certificate verification.
+  required: false
+  default: false
+  type: boolean
+{% endconfiguration %}
+
+It's not possible to create another account in SRM with admin permissions. You'll need to use your admin account (or the one you renamed at creation) for this connection.
+
+List of models known to be supported:
+
+- RT1900ac
+- RT2600ac
+
+See the [device tracker component page](/components/device_tracker/) for instructions on how to configure the people to be tracked.