Add xformers install command to readme and colab notebook.

README.md

@@ -50,6 +50,8 @@ Nvidia users should install torch using this command:
 
 Nvidia users should also install Xformers for a speed boost but can still run the software without it.
 
+```pip install xformers```
+
 #### Troubleshooting
 
 If you get the "Torch not compiled with CUDA enabled" error, uninstall torch with:

notebooks/comfyui_colab.ipynb

@@ -35,7 +35,8 @@
       "source": [
         "!git clone https://github.com/comfyanonymous/ComfyUI\n",
         "%cd ComfyUI\n",
-        "!pip install -r requirements.txt"
+        "!pip install -r requirements.txt\n",
+        "!pip install xformers"
       ]
     },
     {