Add FeII README.md, show datasets in data/README

data/README_data.md

@@ -46,6 +46,18 @@ databases, namely:
 
 See the respective papers for details.
 
+The commands
+```
+database [chianti|stout|lamda]
+```
+are provided to manipulate each database en masse, while the command
+```
+species "Fe+" [dataset="Tayal18"]
+```
+is provided for refined control of individual model ions.
+Notice that the keyword ```dataset``` may be used to select between various
+datasets, as in the Fe+ example above.
+
 
 * * *
 

data/stout/fe/fe_2/README.md

+## Notes
+
+Several datasets are provided for FeII.
+The default at the moment is the old Verner et al. (1999) model, which uses
+the gbar approximation for collision strengths.
+Available are also recent, more accurate calculations by
+[Smyth et al. (2019)](https://ui.adsabs.harvard.edu/abs/2019MNRAS.483..654S),
+[Bautista et al. (2015)](https://ui.adsabs.harvard.edu/abs/2015ApJ...808..174B),
+and
+[Tayal et al. (2018)](https://ui.adsabs.harvard.edu/abs/2018PhRvA..98a2706T).
+
+[Sarkar et al. (2021)](https://ui.adsabs.harvard.edu/abs/2021ApJ...907...12S)
+compare these models and find that the Smyth19 model gives the best results.
+
+To switch between various datasets, follow the instructions in the
+[README file found in the data directory](../../../README_data.md).