Remove "early-release beta" disclaimer from README (#15136)
Summary:
Now that PyTorch 1.0 is out, this should be updated :)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/15136
Differential Revision: D13447377
Pulled By: soumith
fbshipit-source-id: bd4e662c53d0699f25d4d90c1b4c1e182b4427c2
