add mkdocs

docs/widgets/services/proxmoxbackupserver.md

@@ -0,0 +1,14 @@
+---
+title: Proxmox Backup Server
+description: Proxmox Backup Server Widget Configuration
+---
+
+Allowed fields: `["datastore_usage", "failed_tasks_24h", "cpu_usage", "memory_usage"]`.
+
+```yaml
+widget:
+    type: proxmoxbackupserver
+    url: https://proxmoxbackupserver.host:port
+    username: api_token_id
+    password: api_token_secret
+```