minor edits to README - mostly linking to arxiv paper

README.rst

@@ -10,6 +10,6 @@ In addition to calculating how much light is transmitted and reflected, the prog
 
 It can also calculate the parameters measured in ellipsometry. It can also calculate the RGB or xyY color of a multilayer thin film (this requires colorpy, https://pypi.python.org/pypi/colorpy).
 
-For more information, see `manual.pdf <https://github.com/sbyrnes321/tmm/blob/master/manual.pdf>`_. For the list of all functions and how to call them, browse the source code or go to https://pythonhosted.org/tmm/
+For more information, see `manual.pdf <https://github.com/sbyrnes321/tmm/blob/master/manual.pdf>`_. For the list of all functions and how to call them, browse the source code or go to https://pythonhosted.org/tmm/ . For physics-based explanations and derivations of the various formulas calculated by this package, see: https://arxiv.org/abs/1603.02720 .
 
-Tested in Python 3. It probably works in Python 2, or maybe not, I haven't checked in a while. If you want to do color calculations in Python 3, you need to use the Python-3-compatible version of colorpy `here <https://github.com/fish2000/ColorPy/>`_.
+Tested in Python 3. It probably works in Python 2, or maybe not, I haven't checked in a long time. If you want to do color calculations in Python 3, you need to use the Python-3-compatible version of colorpy `here <https://github.com/fish2000/ColorPy/>`_.