docs: introduced C++ google style guide summary

[dudujuju828]

Description

• Adds a concise reference guide for Google's C++ style conventions, following the established format of existing code style guides in the repository.

Changes

• New file summarizing the Google C++ Style Guide
• Covers 8 key areas: Naming, Header Files, Formatting, Classes, Functions, Scoping, Modern C++ Features, and Best Practices

Approach

• Distilled the full guide into actionable, quick-reference rules
• Maintained consistency with other style guide summaries in this repo
• Prioritized the most commonly referenced conventions while preserving important exceptions and edge cases

[sherzat3]

Thanks for sending a PR! Left one minor comment.