Update doc/OnlineDocs/explanation/analysis/doe/guide.rst

Co-authored-by: John Siirola <jsiirola@users.noreply.github.com>

Author: slilonfe5

doc/OnlineDocs/explanation/analysis/doe/guide.rst

@@ -4,7 +4,7 @@ Quick Start Guide
 =================
 
 To use Pyomo.DoE, a user must implement a subclass of the :ref:`Parmest <parmest>` ``Experiment`` class.
-The subclass must have a ``get_labeled_model`` method which returns a Pyomo `ConcreteModel`
+The subclass must have a ``get_labeled_model`` method which returns a Pyomo :class:`ConcreteModel`
 containing four Pyomo ``Suffix`` components identifying the parts of the model used in
 MBDoE analysis. This is in line with the convention used in the parameter estimation tool,
 :ref:`Parmest <parmest>`. The four Pyomo ``Suffix`` components are: