Update index.rst

Application GMC/index.rst

+Application GMC
+==============
+
+.. toctree::
+   :maxdepth: 2
+
+   Application GMC/GMC_Manuel-utilisateur/index_gmc-user.rst
+
+
+.. toctree::
+      :maxdepth: 2
+
+   Application GMC/Modeles_de_donnees/index_modeles-donnees.rst