Add Netlify _redirects file

This ensures the URLs can be navigated to directly.

Tested in ember-learn/super-rentals#146

---

Commit:  ember-learn/super-rentals-tutorial@ba546ad
Script:  https://github.com/ember-learn/super-rentals-tutorial/blob/ba546ade32f43c118706d878a8b8250191ccf4bb/.github/workflows/build.yml
Logs:    https://github.com/ember-learn/super-rentals-tutorial/commit/ba546ade32f43c118706d878a8b8250191ccf4bb/checks

guides/release/tutorial/part-1/orientation.md

@@ -123,6 +123,7 @@ super-rentals
 │   ├── optional-features.json
 │   └── targets.js
 ├── public
+│   ├── _redirects
 │   └── robots.txt
 ├── tests
 │   ├── helpers
@@ -149,7 +150,7 @@ super-rentals
 ├── package-lock.json
 └── testem.js
 
-15 directories, 32 files
+15 directories, 33 files
 ```
 
 We'll learn about the purposes of these files and folders as we go. For now, just know that we'll spend most of our time working within the `app` folder.

guides/release/tutorial/part-1/working-with-data.md

@@ -239,9 +239,10 @@ public
 ├── assets
 │   └── images
 │       └── teaching-tomster.png
+├── _redirects
 └── robots.txt
 
-4 directories, 6 files
+4 directories, 7 files
 ```
 
 You can verify that everything is working correctly by navigating to `http://localhost:4200/api/rentals.json`.