Update readme.md

Author: jgillis

readme.md

@@ -119,7 +119,7 @@ OMG-tools is written in Python 2.7 and depends on the packages numpy, scipy and
 
 `sudo apt-get install python-numpy python-scipy python-matplotlib`
 
-It uses [CasADi](http://casadi.org) as a framework for symbolic computations and interface to IPOPT, a software package for large-scale nonlinear optimization. For installation instructions regarding these software packages, the user is referred to the [CasADi installation page](http://install.casadi.org). The current implementation of this toolbox relies on CasADi 3.1. In the examples, we use the [HSL linear solvers](https://github.com/casadi/casadi/wiki/Obtaining-HSL), as they result in a much faster execution.
+It uses [CasADi](http://casadi.org) as a framework for symbolic computations and interface to IPOPT, a software package for large-scale nonlinear optimization. The current implementation of this toolbox relies on CasADi 3.1, which can be obtained from its [install page](http://install31.casadi.org). In the examples, we use the [HSL linear solvers](https://github.com/casadi/casadi/wiki/Obtaining-HSL), as they result in a much faster execution.
 
 If you want to save your simulation results in Tikz-format, you need [matplotlib2tikz](https://github.com/nschloe/matplotlib2tikz).