Documentation: add info re pfSense API token auth (#3145)

docs/widgets/services/pfsense.md

@@ -9,9 +9,9 @@ This widget requires the installation of the [pfsense-api](https://github.com/ja
 
 Once pfSense API is installed, you can set the API to be read-only in System > API > Settings.
 
-Currently the only supported authentication mode is 'Local Database'.
+There are two currently supported authentication modes: 'Local Database' and 'API Token'. For 'Local Database', use `username` and `password` with the credentials of an admin user. For 'API Token', utilize the `headers` parameter with `client_token` and `client_id` obtained from pfSense as shown below. Do not use both headers and username / password.
 
-WAN interface to monitor can be defined by updating the `wan` param.
+The interface to monitor is defined by updating the `wan` parameter. It should be referenced as it is shown under Interfaces > Assignments in pfSense.
 
 Load is returned instead of cpu utilization. This is a limitation in the pfSense API due to the complexity of this calculation. This may become available in future versions.
 
@@ -21,7 +21,10 @@ Allowed fields: `["load", "memory", "temp", "wanStatus", "wanIP", "disk"]` (maxi
 widget:
   type: pfsense
   url: http://pfsense.host.or.ip:port
-  username: user
-  password: pass
+  username: user # optional, or API token
+  password: pass # optional, or API token
+  headers: # optional, or username/password
+    Authorization: client_id client_token
   wan: igb0
+  fields: ["load", "memory", "temp", "wanStatus"] # optional
 ```