(docs) Update second half of seq.md, structural changes (#3026)

* Update second half of seq.md, structural changes

* Apply suggestions from code review

Commit updates by @cuihtlauac

Co-authored-by: Cuihtlauac Alvarado <[email protected]>

* Move mental model for Seq.{C,c}ons from beginning to end of section

* Apply suggestions from code review

* Apply suggestions from code review

* editing

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Co-authored-by: Cuihtlauac Alvarado <[email protected]>
Co-authored-by: sabine <[email protected]>

Author: 3 people