DOC: Unsuppress relevant dataframe in split-apply-combine guide

[chrisyeh96]

Currently, the user guide for groupby shows the following code, but it is unclear where the "C" and "D" columns come from.

In the rendered documentation, the preceding definition of df does not have "C" and "D" columns.

In [50]: arrays = [
   ....:     ["bar", "bar", "baz", "baz", "foo", "foo", "qux", "qux"],
   ....:     ["one", "two", "one", "two", "one", "two", "one", "two"],
   ....: ]
   ....: 

In [51]: index = pd.MultiIndex.from_arrays(arrays, names=["first", "second"])

In [52]: df = pd.DataFrame({"A": [1, 1, 1, 1, 2, 2, 3, 3], "B": np.arange(8)}, index=index)

In [53]: df
Out[53]: 
              A  B
first second      
bar   one     1  0
      two     1  1
baz   one     1  2
      two     1  3
foo   one     2  4
      two     2  5
qux   one     3  6
      two     3  7

Instead, the code under the heading "DataFrame column selection in GroupBy" is referring to a completely different dataframe which is in the RST file but is suppressed in the rendered documentation.

This pull request un-suppresses that relevant dataframe so that readers can see where the "C" and "D" columns come from.

[mroeschke]

Nice catch. LGTM

[rhshadrach]

lgtm

[rhshadrach]

Thanks @chrisyeh96!