Add stubs on calibration and PySB modules to tutorial (#509)

doc/tutorial.rst

@@ -879,9 +879,16 @@ interacts with the protein *Bak* (residing in the membrane).
 Model calibration
 =================
 
+One option for model calibration in PySB is `PyDREAM`_, which is an
+implementation of the DREAM algorithm developed by Vrugt and ter Braak
+(2008) and Laloy and Vrugt (2012).
+
 Modules
 =======
 
+See :doc:`/modules/index` for further details on the various PySB
+modules and the options available.
+
 Miscellaneous
 =============
 
@@ -944,3 +951,5 @@ hierarchical name of the module from which ``Model()`` is called, e.g.
 .. _GraphViz: http://www.graphviz.org/
 
 .. _OmniGraffle: http://www.omnigroup.com/products/omnigraffle/
+
+.. _PyDREAM: https://pubmed.ncbi.nlm.nih.gov/29028896/