[UsernameTaker]

Description

What changed? The analogy for stage 1b to explain coroutines was changed from taking a sip from a bottle while doing homework to people bowling in a bowling alley
Why? (the code + comments should speak for itself on the "how") The water bottle analogy was not effective enough in describing the commands running in parallel and how they take turns.

We highly recommend including screenshots or a video of what was changed, to collect evidence in a place where we can later reference it.

Any issues this pull request closes or pull requests this supersedes should be linked with Closes #issuenumber.
Closes #399

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Merge checklist:

• Pull Request title is short, imperative summary of proposed changes
• The description documents the what and why, including events that led to this PR
• Pull Request has been linted and formatted and follows the styleguide

[github-actions]

🌐 Preview URL: https://pr-401.frcsoftware.org

Changed pages

• /learning-course/stage1/stage1b/the-command-body/
• /zh-cn/learning-course/stage1/stage1b/the-command-body/