update magma instructions (pytorch#18410)

Summary:
fixes pytorch#18389

cc: stas00
Pull Request resolved: pytorch#18410

Differential Revision: D14594198

Pulled By: soumith

fbshipit-source-id: fb46ef77a36c90ad95e47f7066f5d32aa1f1370f

Author: soumith

Diff for: README.md

@@ -156,7 +156,7 @@ conda install numpy pyyaml mkl mkl-include setuptools cmake cffi typing
 On Linux
 ```bash
 # Add LAPACK support for the GPU if needed
-conda install -c pytorch magma-cuda92 # or [magma-cuda80 | magma-cuda91] depending on your cuda version
+conda install -c pytorch magma-cuda90 # or [magma-cuda80 | magma-cuda92 | magma-cuda100 ] depending on your cuda version
 ```
 
 #### Get the PyTorch Source