Add some instructions how to use the venv from another SD install.

README.md

@@ -44,6 +44,22 @@ Install the dependencies by opening your terminal inside the ComfyUI folder and:
 
 ```pip install -r requirements.txt```
 
+After this you should have everything installed and can proceed to running ComfyUI.
+
+
+#### I already have another UI for Stable Diffusion installed do I really have to install all of these dependencies?
+
+You don't. If you have another UI installed and working with it's own python venv you can use that venv to run ComfyUI. You can open up your favorite terminal and activate it:
+
+```source path_to_other_sd_gui/venv/bin/activate```
+
+or on Windows:
+
+With Powershell: ```"path_to_other_sd_gui\venv\Scripts\Activate.ps1"```
+
+With cmd.exe: ```"path_to_other_sd_gui\venv\Scripts\activate.bat"```
+
+And then you can use that terminal to run Comfyui without installing any dependencies. Note that the venv folder might be called something else depending on the SD UI.
 
 
 # Running