nothing beter to do, added docs for string type

src/interpreter/value/string.rs

@@ -1,5 +1,8 @@
 use std::{fmt::Display, ops::Deref, rc::Rc};
 
+/// A Wisp string type which can hold two variants:
+/// - Borrowed (usually a reference to source code or built-in literal)
+/// - Shared (Ref-counted pointer to [`str`])
 #[derive(Debug, Clone)]
 pub enum Str<'a> {
     Borrowed(&'a str),