Mention magma-cuda101 package in install instructions (#27325)
Summary:
There is a magma package for the newest CUDA verson (10.1), mention it here lest someone try to mistakenly use the version for CUDA 10.0.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/27325
Differential Revision: D17749535
Pulled By: soumith
fbshipit-source-id: 2d34a7af1218e6157935bfd5e03f4d2c0f00f200
