Update README.md

Added short explanation of Fortran libraries and link to python wrapper.

README.md

@@ -3,9 +3,15 @@ Wigner Symbols
 
 A C++ ensemble of functions to compute the Wigner 3j- and 6j- symbols. It reimplements the algorithm designed
 by Schulten and Gordon in C++, but also contains the original Fortran implementation. 
+It can act either as a complelte C++ replacement to the original Fortran implementation, 
+or a C++ interface to them. See the API docs for details. 
 It can either compute an array of Wigner 3j or 6j symbols, or a single
 coefficient. It also computes the Clebsch-Gordan coefficients.
 
+Note that there is a third party [Python wrapper](https://github.com/jeffzhen/wignerpy) 
+available on GitHub.
+
+
 ## Compilation Instructions
 This library uses CMake to help the build process. First, download the source code. 
 It is recommended to create a separate directory for building, i.e.