Adding sass book(pdf)

[BulegaHassan]

What does this PR do?

Add resource(s)

For resources

Description

A free ebook about sass(css preprocessor) with content extracted from Stack Overflow documentation

Why is this valuable (or not)?

• sass is the leading css preprocessor and the book succinctly shows what one needs to know about it.
• Its Contributors are from Stack Overflow

How do we know it's really free?

• The content is released under Creative Commons BY-SA and the list of contributors to each
  chapter are provided in the credits section at the end of this book.

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

Its a book(pdf).

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!

[eshellman]

See #6153

[eshellman]

Thanks, and welcome to free-programming-books!

[BulegaHassan]

Welcome.

Its my first community contribution.