Described default centre argument behaviour in rolling functions (#9819)

* Described default centre argument behaviour in rolling functions.

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xarray/core/dataarray.py

@@ -7081,7 +7081,8 @@ def rolling(
             (otherwise result is NA). The default, None, is equivalent to
             setting min_periods equal to the size of the window.
         center : bool or Mapping to int, default: False
-            Set the labels at the center of the window.
+            Set the labels at the center of the window. The default, False,
+            sets the labels at the right edge of the window.
         **window_kwargs : optional
             The keyword arguments form of ``dim``.
             One of dim or window_kwargs must be provided.

xarray/core/dataset.py

@@ -10728,7 +10728,8 @@ def rolling(
             (otherwise result is NA). The default, None, is equivalent to
             setting min_periods equal to the size of the window.
         center : bool or Mapping to int, default: False
-            Set the labels at the center of the window.
+            Set the labels at the center of the window. The default, False,
+            sets the labels at the right edge of the window.
         **window_kwargs : optional
             The keyword arguments form of ``dim``.
             One of dim or window_kwargs must be provided.

xarray/core/rolling.py

@@ -282,7 +282,8 @@ def __init__(
             (otherwise result is NA). The default, None, is equivalent to
             setting min_periods equal to the size of the window.
         center : bool, default: False
-            Set the labels at the center of the window.
+            Set the labels at the center of the window. The default, False,
+            sets the labels at the right edge of the window.
 
         Returns
         -------
@@ -793,7 +794,8 @@ def __init__(
             (otherwise result is NA). The default, None, is equivalent to
             setting min_periods equal to the size of the window.
         center : bool or mapping of hashable to bool, default: False
-            Set the labels at the center of the window.
+            Set the labels at the center of the window. The default, False,
+            sets the labels at the right edge of the window.
 
         Returns
         -------