add better description to calc_error options

Author: TomDonoghue

fooof/objs/fit.py

@@ -1108,7 +1108,10 @@ def _calc_error(self, metric=None):
         Parameters
         ----------
         metric : {'MAE', 'MSE', 'RMSE'}, optional
-            Which error measure to calculate.
+            Which error measure to calculate:
+            * 'MAE' : mean absolute error
+            * 'MSE' : mean squared error
+            * 'RMSE' : root mean squared error
 
         Raises
         ------