Update note on custom metric name convention

docs/examples/monitoring-kwollect.rst

@@ -78,6 +78,8 @@ This simple payload found in the artifacst directory is a simple bash script exp
 
 .. note::
 
+    If your change the name of the metric from ``my_e2clab_metric`` to any other name, make sure that new name validates the regular exression in the ``monitor`` section of the :ref:`layers_services.yaml` file, otherwise it will not be collected.
+
     To kwow more about custom metrics and at what timestamp they are recorded, check the **Pushing custom metrics** section in the `kwollect documentation`_.
 
 Layers & Services Configuration