Add concrete documentation example for plot_waterfall

Agent-Logs-Url: https://github.com/sdpython/teachpyx/sessions/242bb04a-1d52-4f54-a254-e242a90f9ed5

Co-authored-by: xadupre <22452781+xadupre@users.noreply.github.com>

Author: Copilot

_doc/api/tools/pandas.rst

@@ -2,6 +2,24 @@
 teachpyx.tools.pandas
 =====================
 
+Exemple
+-------
+
+.. plot::
+
+    import pandas
+    import matplotlib.pyplot as plt
+    from teachpyx.tools.pandas import plot_waterfall
+
+    plt.close("all")
+
+    df = pandas.DataFrame({"name": ["A", "B", "C"], "delta": [10, -3, 5]})
+    ax, _ = plot_waterfall(df, "delta", "name", total_label="TOTAL")
+    ax.set_title("Exemple de waterfall")
+    plt.xticks(rotation=30, ha="right")
+    plt.tight_layout()
+    plt.show()
+
 .. automodule:: teachpyx.tools.pandas
     :members:
     :no-undoc-members: