RF: Added link to Numpy website in README

Author: Félix C. Morency

README.rst

@@ -15,9 +15,10 @@ PyNIfTI_.
 .. _MINC: http://wiki.bic.mni.mcgill.ca/index.php/MINC
 .. _PyNIfTI: http://niftilib.sourceforge.net/pynifti/
 .. _GIFTI: http://www.nitrc.org/projects/gifti
+.. _Numpy: http://numpy.scipy.org/
 
 The various image format classes give full or selective access to header (meta)
-information and access to the image data is made available via NumPy arrays.
+information and access to the image data is made available via NumPy_ arrays.
 
 Website
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