DOC: added "How to read these guides" section to User Guide page (#39130)

doc/source/user_guide/index.rst

@@ -17,6 +17,43 @@ For a high level summary of the pandas fundamentals, see :ref:`dsintro` and :ref
 Further information on any specific method can be obtained in the
 :ref:`api`.
 
+How to read these guides
+------------------------
+In these guides you will see input code inside code blocks such as:
+
+::
+
+    import pandas as pd
+    pd.DataFrame({'A': [1, 2, 3]})
+
+
+or:
+
+.. ipython:: python
+
+    import pandas as pd
+    pd.DataFrame({'A': [1, 2, 3]})
+
+The first block is a standard python input, while in the second the ``In [1]:`` indicates the input is inside a `notebook <https://jupyter.org>`__. In Jupyter Notebooks the last line is printed and plots are shown inline.
+
+For example:
+
+.. ipython:: python
+
+    a = 1
+    a
+is equivalent to:
+
+::
+
+    a = 1
+    print(a)
+
+
+
+Guides
+-------
+
 .. If you update this toctree, also update the manual toctree in the
    main index.rst.template