.get() method information added as markdown file

[wearesoback]

Description

Created a new Markdown documentation entry for the .get() method under the topic of smart pointers in C++.

Issue Solved

Closes #6871

Type of Change

• Adding a new entry

Checklist

• [X] All writings are my own.
• [X] My entry follows the Codecademy Docs style guide.
• [X] My changes generate no new warnings.
• [X] I have performed a self-review of my own writing and code.
• [ ] I have checked my entry and corrected any misspellings.
• [ ] I have made corresponding changes to the documentation if needed.
• [ ] I have confirmed my changes are not being pushed from my forked main branch.
• [ ] I have confirmed that I'm pushing from a new branch named after the changes I'm making.
• [ ] I have linked any issues that are relevant to this PR in the Issues Solved section.