Address review

Author: oli-obk

src/SUMMARY.md

@@ -20,6 +20,7 @@
 - [Macro expansion](./macro-expansion.md)
 - [Name resolution](./name-resolution.md)
 - [The HIR (High-level IR)](./hir.md)
+    - [Lowering AST to HIR](./lowering.md)
 - [The `ty` module: representing types](./ty.md)
 - [Type inference](./type-inference.md)
 - [Trait solving (old-style)](./traits/resolution.md)

src/hir.md

@@ -3,7 +3,8 @@
 The HIR – "High-Level Intermediate Representation" – is the primary IR used in
 most of rustc. It is a compiler-friendly representation of the abstract syntax
 tree (AST) that is generated after parsing, macro expansion, and name
-resolution. Many parts of HIR resemble Rust surface syntax quite closely, with
+resolution (see [Lowering](./lowering.md) for how the HIR is created).
+Many parts of HIR resemble Rust surface syntax quite closely, with
 the exception that some of Rust's expression forms have been desugared away. For
 example, `for` loops are converted into a `loop` and do not appear in the HIR.
 This makes HIR more amenable to analysis than a normal AST.