DOC: Fix min_count docstring (pandas-dev#19005)

[ci skip]

(cherry picked from commit 35443b5)

Author: TomAugspurger

pandas/core/generic.py

@@ -7263,7 +7263,7 @@ def _doc_parms(cls):
 
 
 _min_count_stub = """\
-min_count : int, default 1
+min_count : int, default 0
     The required number of valid values to perform the operation. If fewer than
     ``min_count`` non-NA values are present the result will be NA.