update exog params doc

docs/book/content/calibration/exogenous_parameters.md

@@ -14,9 +14,8 @@ kernelspec:
 (Chap_Exog)=
 # Exogenous Parameters
 
-  [TODO: This chapter needs heavy updating. Would be nice to do something similar to API chapter. But it is also nice to have references and descriptions as in the table below.]
+  The JSON file [`ogusa_default_parameters.json`](https://github.com/PSLmodels/OG-USA/blob/master/ogusa/default_parameters.json) provides values for all the model parameters used as defaults for OG-USA. Below, we provide a table highlighting some of the parameters describing the scale of the model (number of periods, aged, productivity types) and some parameters of the solution method (dampening parameter for TPI). The table below provides a list of the exogenous parameters and their baseline calibration values.
 
-  In this chapter, list the exogenous inputs to the model, options, and where the values come from (weak calibration vs. strong calibration). Point to the respective chapters for some of the inputs. Mention the code in [`default_parameters.json`](https://github.com/PSLmodels/OG-USA/blob/master/ogusa/default_parameters.json) and [`parameters.py`](https://github.com/PSLmodels/OG-USA/blob/master/ogusa/parameters.py).
 
   <!-- +++
   ```{code-cell} ogusa-dev