add manual info for nested approximation (#1573)

* Make partial first draft of nested approx manual content.
Move Laplace to "Other Algos" chapter.

* Add more nested approx manual text, focused on
partial draft of usage and node selection.

* Add manual section on nested approx.
Move Laplace to Other Algos chapter.

* Make a few edits to nested approx manual text.

* small tweaks in chapter_AD.Rmd

* Separate Laplace/AGHQ from other algorithms manual chapter.

* Add Laplace chapter file.

* Fix some typos in Laplace manual chapter.

* Fine-tune Laplace chapter, including reparameterize penicillin example.

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Co-authored-by: perrydv <[email protected]>

Author: paciorek