Add example where there is no variable of importance

[lionelkusch]

I think that we should check with an example, the case where there is no variable of importance and identify if the model provides one or not.
I think that the dimension of features and dimension of data will have an impact on this use case. It will be interesting to see if the model is stable over the scaling of this dimension.

[bthirion]

Indeed, it is good to study the behavior of models under the global null, as a sanity check.