Add "Write Graph Representations in C++"

[andrewfaircloth]

Motivation and Context

Adding tutorial for graphs in C++

How Has This Been Tested?

Tested the links to see if they're working correctly Tested code in console for correct output

Types of changes

• [x] New Article (change which adds functionality)

Checklist:

• [x] My code follows the code style of this project.
• [x] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [x] I have made checks to ensure URLs and other resources are valid