Add info in readme that dataset has to be ml-matrix

[vorg]

No description provided.

[targos]

This is wrong. The dataset should be converted internally if it's not a ml-matrix object.
@JeffersonH44 you should be able to use Matrix.checkMatrix for this purpose.

[JeffersonH44]

But I'm seeing the code now and there is no need of the ml-matrix because the algorithm check if the dataset is instance of matrix I just forget it, I will change the doc.