docs: Change 'cursor' to 'agent cursor' in init command

[ruanLN]

Updated the command for initializing Cursor agent.

Summary

• --cursor isn't recognised as a command --agent cursor install the hooks correctly

Test plan

• [N/A] cargo fmt --all && cargo clippy --all-targets && cargo test
• Manual testing: rtk <command> output inspected

Important: All PRs must target the develop branch (not master).
See CONTRIBUTING.md for details.

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[ruanLN]

note, --copilot and --gemini seems to work, so haven't changed them