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MINOR: [Docs] Tweak text on docs index page (#38695)

### Rationale for this change

These are just some minor style tweaks which made the text and buttons on these cards read more naturally to me. Feel free to ignore or take only some of the changes here.

### Are these changes tested?

Yes, I confirmed the docs still build as expected locally.

### Are there any user-facing changes?

New language in docs, see above.

Authored-by: Bryce Mecum <petridish@gmail.com>
Signed-off-by: AlenkaF <frim.alenka@gmail.com>