Add timeout parameter to the example (#80921)

Adding the http timeout parameter to the example to know where  is needed in the yaml configuration.

docs/sources/datasources/loki/_index.md

@@ -60,6 +60,7 @@ datasources:
     access: proxy
     url: http://localhost:3100
     jsonData:
+      timeout: 60
       maxLines: 1000
 ```