Code of Conduct link doesn't work in README.md

[benlenjamin]

The Code of Conduct linked in the Readme.md does not redirect to the ml-agents/CODE_OF_CONDUCT.md, but instead to the ml-agents/docs/CODE_OF_CONDUCT.md (which has no information).

Steps to reproduce the behavior:

1. Go to the Readme,md on the ML-Agents overview/homepage.
2. Scroll down to the bottom section (Community and Feedback).
3. Click on the hyperlink "code of conduct".
4. See error (incorrect file, just displays a file name)

Current Link: https://github.com/Unity-Technologies/ml-agents/blob/develop/docs/CODE_OF_CONDUCT.md
Correct Link: https://github.com/Unity-Technologies/ml-agents/blob/develop/CODE_OF_CONDUCT.md