Update Expo references in React Native docs

[krollins-mdb]

Pull Request Info

We got some docs feedback about Expo. We weren't giving enough indication of where Expo users should look for information.

This PR shuffles some content and provides better sign posting for Expo users.

Staged Changes

• Install Realm
• Bootstrap with Expo
• Use @realm/react

Review Guidelines

REVIEWING.md

Animal Wearing a Hat

[github-actions]

Readability for Commit Hash: d07f2af

You can see any previous Readability scores (if they exist) by looking
at the comment's history.

Readability scores for changed documents:

• source/sdk/react-native/use-realm-react: Grade Level: 10.0, Reading Ease: 54.02
• source/sdk/react-native/bootstrap-with-expo: Grade Level: 12.3, Reading Ease: 48.13
• source/sdk/react-native/install: Grade Level: 10.2, Reading Ease: 42.68

For Grade Level, aim for 8 or below.

For Reading Ease scores, aim for 60 or above:

Score	Difficulty
90-100	Very Easy
80-89	Easy
70-79	Fairly Easy
60-69	Medium
50-59	Fairly Hard
30-49	Hard
0-29	Very Hard

For help improving readability, try Hemingway App.

[lindseymoore]

Small comments, LGTM!

[lindseymoore]

Suggested change

	Create a New App and add ``@realm/react``
	Add ``@realm/react`` to a New App

suggestion for consistency's sake.

[lindseymoore]

Suggested change

	To use the Realm Expo template, follow the :ref:`Quick Start with Expo
	To create a new app with @realm/react using the Realm Expo template, follow the :ref:`Quick Start with Expo

For clarity that the this quick start will also guide through steps of creating new app with @realm/react.

[docs-builder-bot]

✨ Staging URL: https://preview-mongodbmongodb.gatsbyjs.io/realm/master/

🪵 Logs

• job log: cc887f05d67d34166ccad230aa736dc83404a264