message: Clarify implementation details in `README`
diff: @@ -160,7 +160,9 @@ crate, and well... Iced is here!
  As an interesting note, Iced does not rely on reference counting and interior
  mutability at all! There is not a single `Rc`, `RefCell`, or similar used
  -directly in the library.
  +directly in the library. As a consequence, compiler guarantees stay intact and
  +many kinds of filthy bugs and runtime errors are banished. No spooky action at
  +a distance!
  [this pull request]: https://github.com/hecrj/coffee/pull/35
  [`stretch`]: https://github.com/vislyhq/stretch
  