Restore FAQs page

[Folyd]

Summary

I just found that we didn't migrate the FAQs page of the previous website to the new website. I don't know why this happened. However, I strongly suggest we should restore the FAQs page.

Motivation

A FAQs page is pretty useful to all levels of Rustaceans. Especially, it's a good place for a newcomer to have a high-level overview of Rust. For example, Go's FAQs page is helpful for me as a Rustaceans to quickly grasp Go.

Maintenance

Most of the old FAQs can be copied seamlessly to the new ones. However, some are kind of outdated. We also should supplement some new QnAs.