Add note for standard deviation computation

Author: angranl-flex

flow360/component/simulation/outputs/outputs.py

@@ -141,6 +141,9 @@ class MovingStatistic(Flow360BaseModel):
       This means a :py:attr:`moving_window_size`=10 would cover 100 pseudo steps.
       Thus, the :py:attr:`start_step` value is automatically rounded up to
       the nearest multiple of 10 for steady simulations.
+    - When :py:attr:`method` is set to ``"std"``, the standard deviation is computed as a
+      **sample standard deviation** normalized by :math:`n-1` (Bessel's correction), where :math:`n`
+      is the number of data points in the moving window.
 
     Example
     -------