Make comment into a doc comment and change readme ref

Author: mark-i-m

src/librustc/traits/specialize/mod.rs

@@ -8,14 +8,16 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// Logic and data structures related to impl specialization, explained in
-// greater detail below.
-//
-// At the moment, this implementation support only the simple "chain" rule:
-// If any two impls overlap, one must be a strict subset of the other.
-//
-// See traits/README.md for a bit more detail on how specialization
-// fits together with the rest of the trait machinery.
+//! Logic and data structures related to impl specialization, explained in
+//! greater detail below.
+//!
+//! At the moment, this implementation support only the simple "chain" rule:
+//! If any two impls overlap, one must be a strict subset of the other.
+//!
+//! See the [rustc guide] for a bit more detail on how specialization
+//! fits together with the rest of the trait machinery.
+//!
+//! [rustc guide]: https://rust-lang-nursery.github.io/rustc-guide/trait-specialization.html
 
 use super::{SelectionContext, FulfillmentContext};
 use super::util::impl_trait_ref_and_oblig;