Minor clean ups in sidebar and course overview

[Adrianamm]

Description

What changed? Why? (the code + comments should speak for itself on the "how")
For Stage 0, Stage 1, Stage 1, Stage 1A and Stage 1B, the sidebar used the word "Introduction" for the overview. However, the overview page had a header which said "Stage # Overview". I adjusted it so instead of "Stage # Introduction" it is now "Stage # Overview". It's more consistent

The Course overview got small updates, including:

• The list for Stage 0 was out of date. That was updated to reflect what is currently in the stage 0 sidebar
• It was "Stage1A" "Stage1B" but I added a space to keep it consistent. it's now "Stage 1A" and "Stage 1B"
• The sentence for describing 1B was updated to better reflect what it is. also the flow of the setence didn't quite make sense before. Add Command-Based programming, a file structure for programming FRC robots, to kitbot vs Learn Command-Based programming, a file structure for programming FRC robots, by adding it to code written in 1A.
• The link to Stage1 now directs to Stage1 overview. Before it did not

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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

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