Suggestions for RTree documentation (Patch #1656)

RTree is lacking documentation for some of its parameters. I would like to suggest the following small additions to help beginners use RTree more effectively

int max_depth - the depth of the tree. A low value will likely underfit and conversely a high value will likely overfit. The optimal value can be obtained using cross validation or other suitable methods.

min_sample_count - minimum samples required at a leaf node for it to be split. A reasonable value is a small percentage of the total data eg. 1%.

max_categories - is not used (?) (according to my searching of the code)

max_num_of_trees_in_the_forest - The maximum number of trees in the forest (suprise, suprise). Typically the more trees you have the better the accuracy. However, the improvement in accuracy generally diminishes and asymptotes pass a certain number of trees. Also to keep in mind, the number of tree increases the prediction time linearly.

Maybe in the future the documentation should contain a section on using some of the machine learning algorithms. Doesn't have to be in depth, just short useful tips and caveats about each algorithm. I think it would be very useful for beginners.