[Feature Request]: Write docs about undirected graph.

[nayounsang]

About

What is this issue about?

• Existing code or feature
• New code or feature
• Documentation
• working process
• Others

Feature Description

Describe the feature you want to propose in detail.

• Write docs about method.

Why do you want this feature?

Explain why this feature is beneficial for the project or users.

Additional Context

Add any other context or screenshots about the feature request here.