Update README.md

README.md

@@ -15,7 +15,8 @@ Copyright Inria, please read the licence.
   - C++ compiler that supports
     - C++17 [compiler support list](http://en.cppreference.com/w/cpp/compiler_support)
     - [OpenMP](http://www.openmp.org/resources/openmp-compilers/)
-  - Custom BLAS, FFT implementations.
+  - Custom BLAS implementations (MKL, OpenBlas, ...)
+  - [FFTW3](https://www.fftw.org/) library.
 
 The following are optional: