update readme

README.md

@@ -63,7 +63,7 @@ dmipy uses HCP data to illustrate microstructure model examples. To reproduce th
 - [Multi-Compartment Microscopic Diffusion Imaging [Kaden et al. 2016]](https://github.com/AthenaEPI/mipy/blob/master/examples/example_multi_compartment_spherical_mean_technique.ipynb)
 
 ## How to contribute to dmipy
-dmipy's design is completely modular and can easily be extended with new models, distributions or optimizers. To contribute, view our (contribution guidelines)[https://github.com/AthenaEPI/dmipy/blob/master/contribution_guidelines.ipynb].
+dmipy's design is completely modular and can easily be extended with new models, distributions or optimizers. To contribute, view our [contribution guidelines](https://github.com/AthenaEPI/dmipy/blob/master/contribution_guidelines.ipynb).
 ## How to cite dmipy
 Fick, Rutger. *Advanced dMRI signal modeling for tissue microstructure characterization*. Diss. Université Côte d'Azur; Inria Sophia Antipolis, 2017.