Update README with Xcode UI steps for SPM installation

[badrinathvm]

Summary

• Added step-by-step Xcode UI instructions for adding StepperView via Swift Package Manager
• Updated SPM code snippet language from ruby to swift for correct syntax highlighting

Context

A GitHub issue reported that StepperView could not be resolved when installing with SPM. After testing, SPM resolves and builds correctly at version 1.6.7. The README only had Package.swift instructions,
which may have caused confusion for users who add dependencies through Xcode's GUI. Added the more common Xcode workflow to reduce friction.

Type of change

• This change requires a documentation update

Test plan

• Verified SPM resolves StepperView 1.6.7 successfully from a fresh test project
• Verified SPM builds successfully for iOS simulator
• Unit Testing
• UI Testing

Test Configuration

• Xcode version:
• Device/Simulator
• iOS version
• MacOSX version

Checklist:

For checklist items not applicable, mention NA in front of it with some comment if applicable.

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• Add comments to code particularly in hard-to-understand areas
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes before pushing the pull request