[cli] Spell-check and logo update

[rcalixte]

Please confirm this pull request meets the following requirements:

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Editing an existing topic or collection

I'm suggesting these edits to an existing topic or collection:

• Image (and my file is *.png, square, dimensions 288x288, size <= 75 kB)
• Content (and my changes are in index.md)

The correct and consistent spelling is hyphenated. The current logo also struggles to be seen on a dark background. This fixes both issues.

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[ahpook]

Thanks for the fix!