Updating Cuda 12.1/12.4 to 12.4/12.6 to reflect current state (#1794)

* Updating Cuda 12.1/12.4 to 12.4/12.6 to reflect current state

We haven't release 12.1 binaries since 0.7.0 

https://download.pytorch.org/whl/torchao/
https://download.pytorch.org/whl/nightly/torchao/

* Update README.md

Co-authored-by: Andrey Talman <atalman@fb.com>

* Update README.md

---------

Co-authored-by: Andrey Talman <atalman@fb.com>

Author: HDCharles

README.md

@@ -159,20 +159,20 @@ Things we're excited about but need more time to cook in the oven
 
 `torchao` makes liberal use of several new features in Pytorch, it's recommended to use it with the current nightly or latest stable version of PyTorch.
 
-Stable release from Pypi which will default to CUDA 12.1
+Stable release from Pypi which will default to CUDA 12.4
 
 ```Shell
 pip install torchao
 ```
 
 Stable Release from the PyTorch index
 ```Shell
-pip install torchao --extra-index-url https://download.pytorch.org/whl/cu121 # full options are cpu/cu118/cu121/cu124
+pip install torchao --extra-index-url https://download.pytorch.org/whl/cu124 # full options are cpu/cu118/cu124/cu126
 ```
 
 Nightly Release
 ```Shell
-pip install --pre torchao --index-url https://download.pytorch.org/whl/nightly/cu121 # full options are cpu/cu118/cu121/cu124
+pip install --pre torchao --index-url https://download.pytorch.org/whl/nightly/cu126 # full options are cpu/cu118/cu126/cu128
 ```
 
 For *most* developers you probably want to skip building custom C++/CUDA extensions for faster iteration