documentation: update the build instructions for windows

Update install.md to add relevent init command to the windows
compilation steps.

Change-Id: I59be668fbba1f81db7ecfbf80d4ddd2f615eaf57

INSTALL.md

@@ -237,6 +237,10 @@ Only 64-bit MSVC build can be compiled.
 
 - Using a new **Non-Elevated Command Prompt**
 
+```bash
+    python build.py --init --qt <path-to-qt-bin-folder> (e.g. C:/Qt/6.6.2/msvc2019_64)
+```
+
 ```bash
     python build.py --install --qt <path-to-qt-bin-folder> (e.g. C:/Qt/6.6.2/msvc2019_64)
 ```