Edit:: Book for installation in windows

Author: erwinschrodinger1

book/src/installation_windows.md

@@ -29,13 +29,16 @@ When choosing the GTK version to build, select `gtk4` instead of `gtk3`:
 ```
 gvsbuild build gtk4
 ```
-
+<!--  -->
 ### Update `Path` environment variable
 
 2. Update your `Path` environment variable to include the GTK 4 libraries:
    1. Go to settings -> Search and open `Advanced system settings` -> Click on `Environment variables`
    2. Select `Path` -> Click on `Edit` -> Add `C:\gtk-build\gtk\x64\release\bin`
 
+3. Add `New User Variable` in enviroment variable to include `PKG_CONFIG_PATH`:
+   1. Go to settings -> Search and open `Advanced system settings` -> Click on `Environment variables`
+   3. Select `New` -> Input `Variable name` : `PKG_CONFIG_PATH` & `Variable value` : `C:\gtk-build\gtk\x64\release\lib\pkgconfig`
 
 You can now continue with the [project setup](./project_setup.html).