Add express.js handbook authored by Flavio copes

[jaqsparow]

What does this PR do?

Add resource(s)

For resources

Express.js handbook for beginners

Why is this valuable (or not)?

This handbook is a great way for beginner to start learning Express.js concepts.

How do we know it's really free?

This book is completely free and it requires email subscription to get the link to download this book.

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

It is a book

Checklist:

• Read our contributing guidelines
• Search for duplicates.
• Include author(s) and platform where appropriate.
• Put lists in alphabetical order, correct spacing.
• Add needed indications (PDF, access notes, under construction)

Follow-up

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