Links updated

Links used in README.md updated to reflect recent changes in https://developer.kaiostech.com/

KaiOS Developer Portal link changed to https://developer.kaiostech.com/docs/02.getting-started/03.build-your-first-package-app/sample-code#react

os-env-setup link changed to https://developer.kaiostech.com/docs/02.getting-started/01.env-setup/os-env-setup test-your-apps link changed to https://developer.kaiostech.com/docs/02.getting-started/03.build-your-first-package-app/test-your-apps

Result

All links in README.md is working instead of showing the following page