fix dead link. small reword (AMReX-Codes#2400)

Docs/sphinx_documentation/source/index.rst

@@ -24,8 +24,11 @@ etc.  To obtain help, simply post a
 or an `issue <https://github.com/AMReX-Codes/amrex/issues>`_
 on the AMReX GitHub webpage.
 
-There are small stand-alone example codes that demonstrate how to use different parts of the AMReX functionality;
-there is extensive documentation for these tutorial codes at :ref:`amrex_tutorials:amrex_tut_indx`
+To learn AMReX there are walk-through guides and small stand-alone example codes that
+demonstrate how to use different parts of the AMReX functionality. Extensive documentation
+is available at `AMReX Guided Tutorials and Example Codes`_.
+
+.. _`AMReX Guided Tutorials and Example Codes`: https://amrex-codes.github.io/amrex/tutorials_html/
 
 Besides this documentation, there is API documentation generated by `Doxygen
 <https://amrex-codes.github.io/amrex/doxygen>`_.