Drive home the point about feature names

README.md

@@ -476,7 +476,9 @@ serde = { version = "1.0", optional = true }
 
 When we depend on `x`, we can enable the optional Serde dependency with
 `features = ["serde"]`. Similarly we can enable the optional standard library
-dependency with `features = ["std"]`.
+dependency with `features = ["std"]`. The implicit feature inferred by Cargo for
+the optional dependency is called `serde`, not `use-serde` or `with-serde`, so
+we like for explicit features to behave the same way.
 
 As a related note, Cargo requires that features are additive so a feature named
 negatively like `no-abc` is practically never correct.