Eliminating tutorials_index for a link in the sidebar

Author: melissawm

doc/source/user/index.rst

@@ -21,7 +21,7 @@ details are found in :ref:`reference`.
    numpy-for-matlab-users
    building
    c-info
-   tutorials_index
+   NumPy Tutorials <https://numpy.org/numpy-tutorials>
    howtos_index
    depending_on_numpy