Added “Think Python” to free programming books-bg.md

[Vaibhavi45]

Added “Think Python: How to Think Like a Computer Scientist” (by Allen B. Downey) to the Python section of the Bulgarian programming books list.

What does this PR do?

Add resource(s) | Remove resource(s) | Add info | Improve repo

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Description

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Checklist:

• Search for duplicates.
• Include author(s) and platform where appropriate.
• Put lists in alphabetical order, correct spacing.
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[github-actions]

Linter failed, fix the error(s):

free-programming-books/books/free-programming-books-bg.md
50:1-50:11  warning  Incorrect number of blank lines between heading and section  blank-lines-1-0-2  remark-lint
51:1-52:97  warning  Alphabetical ordering: swap l.52 and l.51                    alphabetize-lists  remark-lint

[github-actions]

Linter failed, fix the error(s):

free-programming-books/books/free-programming-books-bg.md
52:1-53:97  warning  Alphabetical ordering: swap l.53 and l.52  alphabetize-lists  remark-lint

[Aniketh78]

Hey @Vaibhavi45, it seems like you have added an English version of the Think Python book to the Bulgarian programming books list. I can't see any Bulgarian copy on the site you have mentioned. Am I missing something? If so, please reply.
Thank you!.