Update README.md

[shawal-mbalire]

Added commands for building the macos desktop application

Description

Please include a summary of the changes along with any relevant motivation and context.

• Closes #
• Fixes #
• Resolves #

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Packaging (updates the packaging)
• Documentation (updates the documentation)

Checklist:

• I have performed a self-review of my code
• I have tested my code in common scenarios and confirmed there are no regressions
• I have added comments to my code, particularly in hard-to-understand sections
• I have made corresponding changes to the documentation
• I have updated and committed pubspec.yaml and pubspec.lock
  • flutter pub get
• I have updated and committed pubspec.lock.json (required for Nix)
  • yq eval pubspec.lock -o=json -P > pubspec.lock.json

yq above is yq-go