link to adjoint docs

Author: dham

demos/shape_optimization/shape_optimization.py.rst

@@ -40,7 +40,7 @@ choose an initial guess (in this case, a unit disc centred at the origin)::
   from firedrake.adjoint import *
   mesh = UnitDiskMesh(refinement_level=3)
 
-Then, we start annotating and turn the mesh coordinates into a control variable::
+Then, we :ref:`start annotating <adjoint-taping>` and turn the mesh coordinates into a control variable::
 
   continue_annotation()
   Q = mesh.coordinates.function_space()

docs/source/adjoint.rst

@@ -159,6 +159,8 @@ The essence of this process is:
    derived automatically by applying UFL's :func:`~ufl.derivative`,
    :func:`~ufl.adjoint`, and :func:`~ufl.action` operators.
 
+.. _adjoint-taping:
+
 Taping an example calculation
 -----------------------------