Add architecture to index postfix for nightly builds (#336)

Author: msaroufim

README.md

@@ -18,9 +18,12 @@ pip install torchao
 ```
 
 Nightly Release
-```Shell 
-pip install --pre torchao-nightly --index-url https://download.pytorch.org/whl/nightly/ # CUDA builds
+```Shell
 pip install --pre torchao-nightly --index-url https://download.pytorch.org/whl/nightly/cpu # CPU only builds
+pip install --pre torchao-nightly --index-url https://download.pytorch.org/whl/nightly/cu118 # CUDA 11.8
+pip install --pre torchao-nightly --index-url https://download.pytorch.org/whl/nightly/cu121 # CUDA 12.1
+pip install --pre torchao-nightly --index-url https://download.pytorch.org/whl/nightly/cu124 # CUDA 12.4
+
 ```
 
 From source