Updated free-courses-en.md

[pcodex]

Updated the Node.js section with a link to a free course on Udemy

What does this PR do?

Add resource(s)

For resources

Description

Updated the Node.js section with a link to a free course on Udemy

Why is this valuable (or not)?

This course will help you get started with Node.js development in under 2 hours

How do we know it's really free?

Labeled as free by Udemy

For book lists, is it a book? For course lists, is it a course? etc.

Course

Checklist:

• [x] Read our contributing guidelines.
• [x] Search for duplicates.
• [x] Include author(s) and platform where appropriate.
• [x] Put lists in alphabetical order, correct spacing.
• [x] Add needed indications (PDF, access notes, under construction).
• [x] Used an informative name for this pull request.

Follow-up

• Check the status of GitHub Actions and resolve any reported warnings!