Add a documentation page for TypeScript FAQ

[aleclarson]

Writing this down as a future improvement. Not near term.

On the fence about whether "type-only information" related to a particular function should be placed at the end of function's page or if we should collect this type-only information into a big TypeScript FAQ page. Similar to how #144 suggests separating functions from types, having a dedicated page for TypeScript technical details could be a good way to hide away the complexity of TypeScript unless you absolutely need it. Some people might prefer to read function pages in their entirety (to ensure they fully understand a function), but those people are unlikely to need the TypeScript-specific information immediately, as TypeScript issues only tend to appear when doing crazy stuff.