Tweak FAQ size profile suggestions

If we want the smallest binary, we probably want codegen-units = 1, and disable incremental builds.

docs/modules/ROOT/pages/faq.adoc

@@ -47,7 +47,8 @@ The first step to managing your binary size is to set up your link:https://doc.r
 debug = false
 lto = true
 opt-level = "s"
-incremental = true
+incremental = false
+codegen-units = 1
 ----
 
 All of these flags are elaborated on in the Rust Book page linked above.