Update the README file

Author: php1ic

README.md

@@ -1,4 +1,29 @@
 # Nuclear Masses
 
-Python package to parse the various files published by the AME and NUBASE.
+## Introduction
+
+Python package to parse the various files published by the [AME](https://www-nds.iaea.org/amdc/) and [NUBASE](http://amdc.in2p3.fr/web/nubase_en.html).
+The files produced by the AME and NUBASE have unique formats so this package does the hard work for you and parses the data into a [pandas dataframe](https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.html) for simple access.
+
+No guarantee is supplied with regards to the accuracy of the data presented.
+Estimated values are included, please always refer to the original sources.
+All data should, however, be accurate.
+
+## Mass tables
+
+The data files released by the papers linked below are used to create the mass tables read by this code
+- [AME2003](https://doi.org/10.1016/j.nuclphysa.2003.11.002) + [NUBASE2003](https://doi.org/10.1016/j.nuclphysa.2003.11.001)
+- [AME2012](https://doi.org/10.1088/1674-1137/36/12/002) + [NUBASE2012](https://doi.org/10.1088/1674-1137/36/12/001)
+- [AME2016](https://doi.org/10.1088/1674-1137/41/3/030002) + [NUBASE2016](https://doi.org/10.1088/1674-1137/41/3/030001)
+- [AME2020](https://doi.org/10.1088/1674-1137/abddaf) + [NUBASE2020](https://doi.org/10.1088/1674-1137/abddae)
+
+The NUBASE files are read for all of the data values, with the AME files being used to populate an additional mass excess data field.
+No comparison or validation is done on common values.
+
+## Setup
+
+The package is available on the Python Package Index so can be installed via pip
+```bash
+pip install nuclearmasses
+```