Add some more docs for serializing strings (#155)

* Add some more docs for serializing strings

Namely, it clarifies that its being serialized under its bytewise
representation. Thought I'd add some comments here, just in case someone
was confused regarding the string encoding

serialize/src/lib.rs

@@ -207,6 +207,9 @@ impl CanonicalDeserialize for usize {
 }
 
 // Implement Serialization for `String`
+// It is serialized by obtaining its byte representation as a Vec<u8> and
+// serializing that. This yields an end serialization of
+// `string.len() || string_bytes`.
 impl CanonicalSerialize for String {
     #[inline]
     fn serialize<W: Write>(&self, mut writer: W) -> Result<(), SerializationError> {