Improved beszel documentation

- Fixed Beszel repo link
- Added information about where to find `systemId`
- Added information about how to set up custom fields

docs/widgets/services/beszel.md

@@ -3,9 +3,9 @@ title: Beszel
 description: Beszel Widget Configuration
 ---
 
-Learn more about [Beszel]()
+Learn more about [Beszel](https://github.com/henrygd/beszel)
 
-The widget has two modes, a single system with detailed info if `systemId` is provided, or an overview of all systems if `systemId` is not provided.
+The widget has two modes, a single system with detailed info if `systemId` is provided, or an overview of all systems if `systemId` is not provided. Note: `systemId` is not the system name. Find the correct ID in the list at `http://beszel.host.or.ip/_/#/collections` under the `id` field.
 
 Allowed fields for 'overview' mode: `["systems", "up"]`
 Allowed fields for a single system: `["name", "status", "updated", "cpu", "memory", "disk", "network"]`
@@ -18,3 +18,13 @@ widget:
   password: password
   systemId: systemId # optional
 ```
+
+To show specific fields for a single system (up to a maximum of 4), add a `fields` to the widget config above. For example:
+
+```yaml
+fields:
+  - cpu
+  - memory
+  - disk
+  - network
+```