Add an FAQ section

[rylev]

The idea would be to give short answers to frequently asked questions that then link to other sections of the book where more thorough answers are given. Some example questions:

• What is the difference between a Wasm component and a Wasm module?
• How do Wasm components and WASI relate to one another?
• I see the terms preview 1 and preview 2 frequently. What do those refer to?
• What are component imports?
• What are component exports?

[kate-goldenring]

+1. We can also add links to Zulip or GH issues to direct people where to ask other questions

[vados-cosmonic]

It might make sense to have some sections be language specific (or a language specific subheading under a general heading?) -- this came up in #151 (but is a very commonly asked question, literally it's been asked 3 times that I know of)