DOC: Fix LabelBinarizer docstring to rst format bug

Also add line to make multilabel classification example more instructive

Before:
![selection_002](https://cloud.githubusercontent.com/assets/1284973/5189062/c35a7a1e-74a8-11e4-93a0-c7888a895bb8.png)

After:
![selection_004](https://cloud.githubusercontent.com/assets/1284973/5189246/095a114a-74aa-11e4-866d-31c3d8707138.png)