docs: add Canadian student internship board

[hanzili]

Hi! Thanks for maintaining this internship guide.

This adds one Canada-specific resource to the startup/internship resources section: Hanzilla Jobs' internships page.

Why it may be useful for readers:

• it is a free, daily-updated Canadian student/recent-grad jobs board;
• it covers internships, co-ops, new grad, junior, and entry-level roles;
• it is broader than software-only: tech, finance, engineering, business, sciences, and more.

Disclosure: I help maintain Hanzilla Jobs. Keeping this as a single line in the existing resources section so it is easy to accept/reject.