Update python/doc/usecases/use_case_stiffened_panel.rst

Co-authored-by: Michael Baudin <31351465+mbaudin47@users.noreply.github.com>

python/doc/usecases/use_case_stiffened_panel.rst

@@ -65,7 +65,7 @@ We assume that the input variables are independent except the :math:`f_1` and
 :math:`f_2` for which we measure a Spearman correlation of :math:`\rho^S_{12}=-0.8`,
 modelled using a :class:`~openturns.NormalCopula`.
 
-The critical load :math:`(\tau_{xy})_{cr}` of a stiffened panel subject to shear load is given by
+The critical load :math:`(\tau_{xy})_{cr}` of a stiffened panel subject to shear load is:
 
 .. math::
   (\tau_{xy})_{cr}=k_{xy}\frac{\pi^2D}{b_0^2t_s}