DOC: update example for adding rows in spreadsheet comparison

Old example was referencing a no-longer-existent variable. Switched to
use `append()` rather than `loc`.

Author: afeld

doc/source/getting_started/comparison/comparison_with_spreadsheets.rst

@@ -416,14 +416,12 @@ The equivalent in pandas:
 Adding a row
 ~~~~~~~~~~~~
 
-To appended a row, we can just assign values to an index using :meth:`~DataFrame.loc`.
-
-NOTE: If the index already exists, the values in that index will be over written.
+Assuming we are using a :class:`~pandas.RangeIndex` (numbered ``0``, ``1``, etc.), we can use :meth:`DataFrame.append` to add a row to the bottom of a ``DataFrame``.
 
 .. ipython:: python
 
-    df1.loc[7] = [8, "tonks"]
-    df1
+    df
+    df.append({"x": 7, "y": 8}, ignore_index=True)
 
 
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