C macros, not C++ templates.

@cmr rightfully points out that C macros are worse, and share the
same name.

src/doc/guide.md

@@ -201,8 +201,8 @@ which is how metaprogramming is done in Rust. If it were a function instead, it
 would look like this: `println()`. For our purposes, we don't need to worry
 about this difference. Just know that sometimes, you'll see a `!`, and that
 means that you're calling a macro instead of a normal function. One last thing
-to mention: Rust's macros are significantly different than C++ templates, if
-you've used those. Don't be scared of using macros. We'll get to the details
+to mention: Rust's macros are significantly different than C macros, if you've
+used those. Don't be scared of using macros. We'll get to the details
 eventually, you'll just have to trust us for now.
 
 Next, `"Hello, world"` is a **string**. Strings are a surprisingly complicated