Update README.md - New URL for "Setting up the development environment"

[theDavidCoen]

The old link doesn't work anymore.

The new one is https://reactnative.dev/docs/environment-setup?package-manager=yarn

CHANGELOG

Does this branch warrant an entry to the CHANGELOG?

• [ ] Yes
• [x] No

Dependencies

none

Requirements

If you have made any visual changes to the GUI. Make sure you have:

• [ ] Tested on iOS device
• [ ] Tested on Android device
• [ ] Tested on small-screen device (iPod Touch)
• [ ] Tested on large-screen device (tablet)