add baseline FAQ and Accordions (#37)

Author: rezrah

.changeset/curvy-guests-tell.md

@@ -0,0 +1,8 @@
+---
+'@primer/react-brand': minor
+---
+
+added an FAQ component, which displays a list of questions and answers relating to a particular subject.
+
+[See usage examples](https://primer.style/react-brand/components/FAQ)
+