transpile: some doc improvements from #1306 (#1336)

* Split out of #1306.

Author: kkysen

c2rust-transpile/src/c_ast/mod.rs

@@ -601,8 +601,8 @@ impl TypedAstContext {
         }
     }
 
-    // Pessimistically try to check if an expression doesn't return. If it does, or we can't tell
-    /// that it doesn't, return `false`.
+    /// Pessimistically try to check if an expression doesn't return.
+    /// If it does, or we can't tell that it doesn't, return `false`.
     pub fn expr_diverges(&self, expr_id: CExprId) -> bool {
         let func_id = match self.index(expr_id).kind {
             CExprKind::Call(_, func_id, _) => func_id,
@@ -1186,6 +1186,9 @@ pub enum OffsetOfKind {
 
 /// Represents an expression in C (6.5 Expressions)
 ///
+/// This is modeled on Clang's APIs, so where documentation
+/// is lacking here, look at Clang.
+///
 /// We've kept a qualified type on every node since Clang has this information available, and since
 /// the semantics of translations of certain constructs often depend on the type of the things they
 /// are given.