Added licenses with proper format and sources

[Antrikshgwal]

What does this PR do?

Add licences with sources

For resources

License Statement: Found on the book’s webpage, which specifies the license as CC BY-NC-SA
Mastering Bitcoin - Unlocking Digital Currencies (2017), 2nd Edition:

License Statement: Found in the GitHub repository README, where it specifies CC BY-NC-ND.
Competitive Programming Handbook by Antti Laaksonen:

License Statement: Found in the book’s Github, specifying the license as CC BY-NC-SA .

Description

Why is this valuable (or not)?

How do we know it's really free?

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

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

Follow-up

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

[github-actions]

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Please 🙏, take a moment and address the merge conflicts of your pull request before we can evaluate it again.

Thanks in advance for your effort and patience ❤️!