DOC: complement the documentation for pandas.DataFrame.agg #35912 (#35941)

* DOC: complement the documentation for pandas.DataFrame.agg

* DOC: complement the documentation for pandas.DataFrame.agg

reformat the documentation according to PEP  8

* DOC: complement the documentation for pandas.DataFrame.agg

reformat the documentation according to PEP 8

Author: onshek

pandas/core/frame.py

@@ -7380,6 +7380,15 @@ def _gotitem(
     min   1.0  2.0
     sum  12.0  NaN
 
+    Aggregate different functions over the columns and rename the index of the resulting
+    DataFrame.
+
+    >>> df.agg(x=('A', max), y=('B', 'min'), z=('C', np.mean))
+         A    B    C
+    x  7.0  NaN  NaN
+    y  NaN  2.0  NaN
+    z  NaN  NaN  6.0
+
     Aggregate over the columns.
 
     >>> df.agg("mean", axis="columns")