Git Basics: Improve clarity of cd git_test command

[MaoShizhong]

Because

It's a somewhat common occurrence where the current wording of step 7 of Git Basics causes a learner to run cd on its own instead of cd git_test as intended. The ensuing confusion should be self-explanatory.

This PR

• Improves clarity of step 7 wording and intended command
• Removes trailing spaces

Issue

N/A

Pull Request Requirements

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[KevinMulhern]

LGTM - thanks as always @MaoShizhong 💪