Improve documentation for RcStr

crates/turbo-tasks/src/rcstr.rs

@@ -12,7 +12,11 @@ use turbo_tasks_hash::{DeterministicHash, DeterministicHasher};
 
 use crate::debug::{ValueDebugFormat, ValueDebugFormatString};
 
-/// This type exists to allow swapping out the underlying string type easily.
+/// A reference counted [`String`], similar to [`Arc<String>`][std::sync::Arc].
+///
+/// This type is intentionally opaque allow for future optimizations to the
+/// underlying representation. Future implementations may use inline
+/// representations or interning.
 //
 // If you want to change the underlying string type to `Arc<str>`, please ensure that you profile
 // performance. The current implementation offers very cheap `String -> RcStr -> String`, meaning we