fix readme link (#1890)
fix readme link (#1890)

Summary:
fix link to self training readme

Pull Request resolved: https://github.com/fairinternal/fairseq-py/pull/1890

Reviewed By: arbabu123, ArmenAg

Differential Revision: D28609910

Pulled By: alexeib

fbshipit-source-id: 4cbbb75cfec876938d80c8d7bc0df4ba93d4f54d

pytorch/fairseq,pytorch/fairseq,pytorch/fairseq