Add Greek (el) C book: "Μια σύγχρονη προσέγγιση στη γλώσσα C"

[Maria-Papa]

What does this PR do?

Add resource(s)

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Description

A Greek-language textbook that introduces the C programming language through modern practices and real-world applications. It covers core syntax, memory management, modular design, debugging techniques, and advanced topics like GUI development and interoperability with Python. Ideal for learners seeking a structured, academically vetted resource with practical depth.

Why is this valuable (or not)?

This is a comprehensive, modern textbook that covers both foundational and advanced topics in C programming. It includes chapters on memory management, data structures, debugging, static/dynamic analysis, GUI development, and C–Python interoperability. It’s ideal for Greek-speaking learners and educators seeking a free, academically vetted resource.

How do we know it's really free?

The book is published by Kallipos, a government-funded open academic publishing platform in Greece. It is distributed under the Creative Commons BY-NC-SA 4.0 license, which permits free access and non-commercial redistribution with attribution.

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

It is a book.

Checklist:

• 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).
• Used an informative name for this pull request.

Follow-up

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

[Maria-Papa]

I noticed the CONTRIBUTING file doesn’t mention formatting guidelines for resources with multiple authors. Could you please review my formatting to confirm it aligns with your expectations?

If it looks good, I suggest opening an issue to clarify how multi-author entries should be handled in future contributions.