Link to pass docs from NRVO module docs

compiler/rustc_mir/src/transform/nrvo.rs

@@ -1,3 +1,5 @@
+//! See the docs for [`RenameReturnPlace`].
+
 use rustc_hir::Mutability;
 use rustc_index::bit_set::HybridBitSet;
 use rustc_middle::mir::visit::{MutVisitor, NonUseContext, PlaceContext, Visitor};