docs: fix material themes path in user stories

Author: PowerKiKi

docs/documentation/stories/include-angular-material.md

@@ -30,13 +30,13 @@ import { MaterialModule } from '@angular/material';
 })
 ```
 
-Now that the project is set up, it must be configured to include the CSS for a theme. Angular Material ships with some prebuilt theming, which is located in `node_modules/@angular/material/core/theming/prebuilt`.
+Now that the project is set up, it must be configured to include the CSS for a theme. Angular Material ships with some prebuilt theming, which is located in `node_modules/@angular/material/prebuilt-themes/`.
 
 To add an angular CSS theme and material icons to your app...
 ```sass
 /* in src/styles.css */
 
-@import '~@angular/material/core/theming/prebuilt/deeppurple-amber.css';
+@import '~@angular/material/prebuilt-themes/deeppurple-amber.css';
 @import '~https://fonts.googleapis.com/icon?family=Material+Icons';
 ```