Add missing directory change step in PR instructions

[zhihali]

Description

issue related: #3969

This update adds a missing step in the pull request instructions that specifies changing into the newly cloned directory before adding a remote origin. This step is essential for new contributors to correctly set up their local repository for subsequent operations and it's better for rookie like myself.

Fixes # (if you have an issue number, include it here)

Type of change

• Documentation update

How Has This Been Tested?

• This change does not alter code but updates documentation. It was visually inspected to ensure clarity and correctness.

Does This PR Require a Contrib Repo Change?

• No.

Checklist:

• Followed the style guidelines of this project
• Documentation has been updated