DOC: add headings to the column selection include

Easier to see what's happening in each line of code, and make navigation
easier.

Author: afeld

doc/source/getting_started/comparison/includes/column_selection.rst

@@ -1,13 +1,23 @@
 The same operations are expressed in pandas below. Note that these operations do not happen in
 place. To make these changes persist, assign the operation back to a variable.
 
+Keep certain columns
+''''''''''''''''''''
+
 .. ipython:: python
 
-   # keep
    tips[["sex", "total_bill", "tip"]]
 
-   # drop
+Drop a column
+'''''''''''''
+
+.. ipython:: python
+
    tips.drop("sex", axis=1)
 
-   # rename
+Rename a column
+'''''''''''''''
+
+.. ipython:: python
+
    tips.rename(columns={"total_bill": "total_bill_2"})