Create an FAQ on common interop topics

[mfeineis]

People who know other languages almost always have the same kind of questions about why Elm chooses to do stuff in specific - usually uncommon - ways. It might be helpful to include an FAQ on the usual topics with links to discourse and elm-discuss/elm-dev (regarding taks ports, FFI, kernel code, etc)

• Do the thing
• Decide whether this should be part of this repo
• put it where it belongs

[mfeineis]

Links I've gathered over time

• Task ports
  • https://discourse.elm-lang.org/t/chadtech-mail-making-ports-act-like-http-requests/1200/4
  • https://groups.google.com/d/msg/elm-dev/kNKilHjUYqo/ZEWOf0mLAgAJ
  • https://discourse.elm-lang.org/t/responses-from-command-ports/2119
  • https://gist.github.com/alpacaaa/13335246234042395813d97af029b10f
  • https://discourse.elm-lang.org/t/responses-from-command-ports/2119/3