Add instruction to set up path to Node

Author: intitni

README.md

@@ -50,7 +50,8 @@ Or install it manually, by downloading the `Copilot for Xcode.app` from the late
 Then set it up with the following steps:
 
 1. Open the app, the app will create a launch agent to setup a background running Service that does the real job.
-2. Enable the extension in `System Settings.app`. 
+2. Optionally setup the path to Node. The default value is just `node`, Copilot for Xcode.app will try to find the Node from `/usr/bin:/usr/local/bin`. If your Node is installed somewhere else, you can run `which node` from terminal to get the path.   
+3. Enable the extension in `System Settings.app`. 
 
     From the Apple menu located in the top-left corner of your screen click `System Settings`. Navigate to `Privacy & Security` then toward the bottom click `Extensions`. Click `Xcode Source Editor` and tick `Copilot`.