feat(errors5): add simpler explanation for box dyn

Author: manyinsects

Cargo.lock

@@ -4,6 +4,8 @@
 
 // This exercise uses some concepts that we won't get to until later in the course, like `Box` and the
 // `From` trait. It's not important to understand them in detail right now, but you can read ahead if you like.
+// For now, think of the `Box<dyn ...>` type as an "I want anything that does ???" type, which, given
+// Rust's usual standards for runtime safety, should strike you as somewhat lenient!
 
 // In short, this particular use case for boxes is for when you want to own a value and you care only that it is a 
 // type which implements a particular trait. To do so, The Box is declared as of type Box<dyn Trait> where Trait is the trait