DOC: Update dependency for to_markdown documentation (#36938)

* Update to_markdown documentation

Adding to the documentation that tabulate is required for to_markdown to be executed

* Move the optional dependency to a note

* Update series.py

* Update series.py

* Update pandas/core/series.py

Co-authored-by: Marco Gorelli <[email protected]>

Co-authored-by: Marco Gorelli <[email protected]>

Author: Eyal Trabelsi

pandas/core/series.py

@@ -1472,6 +1472,10 @@ def to_markdown(
         str
             {klass} in Markdown-friendly format.
 
+        Notes
+        -----
+        Requires the `tabulate <https://pypi.org/project/tabulate>`_ package.
+
         Examples
         --------
         >>> s = pd.Series(["elk", "pig", "dog", "quetzal"], name="animal")