Adding documentation about contrib.losses (#11600)

* Update contrib.lossses.md

Adding note that this module is deprecated

* Update __init__.py

Add spaces so that this shows up well on the website

* Update __init__.py

Alignment does not comply with PEP8, minor cleanup of comments

* Update README.md

Notify readers that this module is deprecated

* Update losses_op.py

-Clarify deprecated information
-Correct minor error
-Minor grammar fixes

* Grammar fix