Add make-whatif page and styles for `code`

Page converted from https://docs.google.com/document/d/1TwihW6LHSJpBrz3bKjDUwgm0eu4PCFWLtEfKdCr1Hnk
and mainly unchanged.

Styles from https://guides.github.com/components/primer/markdown.css
Appropriate rename 'help' page file
Minor changes for 'help' and 'about' pages
Update 'make-whatif' page and exclude 'translations-style'
Next update of 'make-whatif' and 'translations-style' pages