FIX #1512

[devwork260802]

Fix: Dead link in https://ocaml.org/learn/tutorials/introduction_to_gtk.html #1512

Issue Description

The first link in the Introduction to Gtk section is dead. I think the link should lead to https://ocaml.org/learn/tutorials/a_first_hour_with_ocaml.html

Fixes #1512

Changes Made

i have added the link to the word [interactive toplevel]

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