Link to supplemental guide on customizing simulations for research se…

…ttings

Signed-off-by: Lizzie Lundgren <elundgren@seas.harvard.edu>

docs/source/index.rst

@@ -83,6 +83,7 @@ use Spack to install GCHP's dependencies if needed.
    supplement/stretched-grid.rst
    supplement/satellite-overpass.rst
    geos-chem-shared-docs/supplemental-guides/bashdatacatalog.rst
+   geos-chem-shared-docs/supplemental-guides/customize-guide.rst
    geos-chem-shared-docs/supplemental-guides/error-guide.rst
    geos-chem-shared-docs/supplemental-guides/debug-guide.rst
    geos-chem-shared-docs/supplemental-guides/species-guide.rst