gurobi installation docs outdated

[k-dominik]

Our docs point at a script that we do not distribute anymore on mac:

ilastik.github.io/documentation/basics/installation.md

Lines 202 to 203 in f01b40f

	In the next step you have to execute a script that will link your GUROBI libraries to your ilastik installation.
	The script can be found in `your-ilastik-installation-folder/ilastik-meta/ilastik/scripts`.

I've checked and for me using gurobi "just worked"™ - awaiting feedback if this is now the norm on mac (I expect this to work when using default locations). So the script might still be useful.

Related discussion on forum.image.sc