Include `cross-env` as devDependency to the example project

**Is your feature request related to a problem? Please describe.**
It's not exactly a problem, but the usage of environment variables on scripts in the example project does not work on all platforms (e.g. Windows).

**Describe the solution you'd like**
Using `cross-env` package, it would be possible to run on all environments.

**Describe alternatives you've considered**
The alternative is to manually changing the scripts to match your development platform requirements before running any command and being careful not to commit the changes.

**Additional context**
You can check the `cross-env` package on NPM [here](https://www.npmjs.com/package/cross-env). And the scripts could be changed to:

```diff
"scripts": {
"eas-build-pre-install": "cd .. && yarn",
- "start": "EXPO_NO_TYPESCRIPT_SETUP=1 expo start",
- "android": "EXPO_NO_TYPESCRIPT_SETUP=1 expo start --android",
- "android:native": "EXPO_NO_TYPESCRIPT_SETUP=1 expo run:android",
- "ios": "EXPO_NO_TYPESCRIPT_SETUP=1 expo start --ios",
- "web": "EXPO_NO_TYPESCRIPT_SETUP=1 expo start --web"
+ "start": "cross-env EXPO_NO_TYPESCRIPT_SETUP='1' expo start",
+ "android": "cross-env EXPO_NO_TYPESCRIPT_SETUP='1' expo start --android",
+ "android:native": "cross-env EXPO_NO_TYPESCRIPT_SETUP='1' expo run:android",
+ "ios": "cross-env EXPO_NO_TYPESCRIPT_SETUP='1' expo start --ios",
+ "web": "cross-env EXPO_NO_TYPESCRIPT_SETUP='1' expo start --web"
},
```

サンプルプロジェクトのパッケージマニフェストを見つけ、そこに記載されている start、Android、iOS、web スクリプトを確認します。要求された開発依存関係を追加し、影響を受ける各コマンドがクロスプラットフォームの環境変数にそれを使用していることを確認します。

索引モデルが issue の本文から書いたものです。