add exodus installation information to demo doc

exodus install flag not supported in firedrake-update

Author: GregVernon

demos/immersed_fem_cubit/immersed_fem_cubit.py.rst

@@ -12,14 +12,19 @@ please refer to the documentation on the
 Sandia Engineering Analysis Code Access System (SEACAS) project's
 `homepage <https://gsjaardema.github.io/seacas-docs/sphinx/html/index.html>`_ or
 `their GitHub page <https://github.com/gsjaardema/seacas>`_.
+
 While this demo focuses on using CUBIT and/or Coreform Cubit for constructing
 Exodus meshes, the SEACAS page provides utilities and detailed information
 for creating Exodus meshes programmatically.  For example, the user could
 use any mesh-generation library available in Matlab, Python, Julia, C++, Fortran, etc., 
 construct the proper datatype in said language, and then export directly to 
 the Exodus format.  This excercise is left to the reader.
 
-As example, we will construct and mesh a rectangle with a disc
+**Note:** In order to use Exodus files, the Exodus library must first be installed.
+This can be done simply by adding the flag ``--with-exodusii`` to the 
+``firedrake-install`` command.
+
+Beginning the demonstration, we will construct and mesh a rectangle with a disc
 in the middle as shown in the below image
 
 .. image:: immersed_geom_cubit.png

docs/source/variational-problems.rst

@@ -33,6 +33,11 @@ object like so:
 This works in both serial and parallel, Firedrake takes care of
 decomposing the mesh among processors transparently.
 
+**Note:** To read meshes in the Exodus format, you need to build 
+Firedrake with the ``--with-exodusii`` flag in the ``firedrake-install`` command.  
+For more information example and an example of generating an Exodus 
+mesh see: :doc:`Creating Firedrake-compatible meshes in Cubit<demos/immersed_fem_cubit.py>`
+
 Reordering meshes for better performance
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~