[MRG+1] Docs: refer users to the other encoders to do one hot encoding for labels. (#7315)

* refer users to the other encoders to do one hot encoding for labels.

* added to the 'see more' for labelbinarizer, multilabelbinarizer, and labelencoder' as well as an example to multilabel binarizer

* added note about y labels to the OneHotEncoder docstring

* removed example from MultiLabelBinarizer

* documentation should specify LabelBinarizer, not MultiLabelBinarizer in OHE