feat: improve error message when cannot find Xcode project

[szymonrybczak]

Summary:

Guides user to maybe install Cocoapods when Xcode project is not available (there are some project when running pod install generates projects).

Test Plan:

1. Clone the repository and do all the required steps from the Contributing guide
2. Create a project with npx --package react-native-test-app@latest init
3. Run yarn react-native run-ios.

Checklist

• Documentation is up to date to reflect these changes.
• Follows commit message convention described in CONTRIBUTING.md

[thymikee]

Good one