Add some information about the IMRPhenomPv2 bases.

README.md

-# Repository for reduced order quadratures of cbc waveform models for use in parameter estimation
\ No newline at end of file
+# Repository for reduced order quadratures of cbc waveform models for use in parameter estimation
+
+Currently the repository contains bases for the `IMRPhenomPv2` waveform model as
+implemented in [lalsuite](https://git.ligo.org/lscsoft/lalsuite)'s lalsimulation package.
+In subdirectories bases are provided for a number of different segment lengths.
+The construction of these bases is discussed in Smith et al, https://arxiv.org/abs/1604.08253. 
+Please consider adding a citation to this paper if you are using the bases in analyses.