Merge pull request #416 from danwilhelm/traits-readme

feat: Add traits README

exercises/traits/README.md

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+### Traits
+
+A trait is a collection of methods. 
+
+Data types can implement traits. To do so, the methods making up the trait are defined for the data type. For example, the `String` data type implements the `From<&str>` trait. This allows a user to write `String::from("hello")`.
+
+In this way, traits are somewhat similar to Java interfaces and C++ abstract classes.
+
+Some additional common Rust traits include:
+
++ `Clone` (the `clone` method), 
++ `Display` (which allows formatted display via `{}`), and
++ `Debug` (which allows formatted display via `{:?}`).
+
+Because traits indicate shared behavior between data types, they are useful when writing generics.
+
+
+#### Book Sections
+
+- [Traits](https://doc.rust-lang.org/book/ch10-02-traits.html)