Docs: Add instructions for using ng add

Fixes #1739

projects/ngrx.io/content/guide/schematics/install.md

@@ -15,3 +15,29 @@ For more information on using `yarn` check out the docs <a href="https://yarnpkg
 ```sh
 yarn add @ngrx/schematics --dev
 ```
+
+## Make @ngrx/scematics as default for app
+
+You can also make @ngrx/schematics as default for your app. Rub below command inside an angular application from the root.
+
+```sh
+ng add @ngrx/schematics
+```
+
+It will prompt you with:
+
+`Do you want to use @ngrx/schematics as the default collection?(y/n)`
+
+Once you select `yes` you can notice below line added to `package.json`.
+
+`
+"cli": {
+    "defaultCollection": "@ngrx/schematics"
+}`
+
+After this change you are free to use any ngrx schematics without mentioning it
+
+`ng g store State`
+
+the above command will create a reducer file for us. you will notice a new file in `app/reducers`.
+