Added book licenses

[AineshSridhar]

What does this PR do?

Adds license info on the basis of instructions provided under issue #11355

For resources

Description

Added License information to following books:

#License mentioned in the last line of the description

Under books/free-programming-books-langs.md:
Book 530 - Essential C++, Krzysztof Kowalczyk, StackOverflow Contributors
Source: Source
"Content is licensed under Creative Commons Attribution-ShareAlike 3.0."

#Mentioned in the footer of the website and soft copy of book (PDF)

Under books/free-programming-books-subjects.md
Book 745 - UNIX Application and System Programming, lecture notes, Stewart Weiss
Source: UNIX Source 1
"Unless otherwise noted, all content is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License."

2nd Source: UNIX Source 2 (Mentioned in the footer of the 1st page of PDF)
"This work is copyrighted by Stewart Weiss and licensed under the Creative Commons AttributionShareAlike 4.0 International License."

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!

[eshellman]

Thanks, and welcome to free-programming-books!