Update branch creation instructions in CHALLENGES.md

[abinyads-dev]

Rephrase instructions for creating a branch in GitHub.

Summary

Changes

Related Issue

Closes #

How to Review

Accessibility Considerations

• Heading levels are sequential (no skipped levels)
• Link text is descriptive (no "click here" or bare URLs)
• Any images include meaningful alt text, or alt="" if decorative
• No content relies on color alone to convey meaning
• Keyboard navigation still works as expected

Testing

• Tested with:
• Screen reader used (if applicable):
• Browser (if applicable):

Screenshots or Recordings