Update const-eval.md

Author: oli-obk

src/const-eval.md

@@ -34,4 +34,4 @@ integer or fat pointer, it will directly yield the value (via `Value::ByVal` or
 memory allocation (via `Value::ByRef`). This means that the `const_eval`
 function cannot be used to create miri-pointers to the evaluated constant or
 static. If you need that, you need to directly work with the functions in
-`src/librustc_mir/interpret/const_eval.rs`.
+[src/librustc_mir/interpret/const_eval.rs](https://github.com/rust-lang/rust/blob/master/src/librustc_mir/interpret/const_eval.rs).