Make schemars_derive optional

README.md

@@ -203,6 +203,7 @@ fn main() {
 `#[serde(...)]` attributes can be overriden using `#[schemars(...)]` attributes, which behave identically (e.g. `#[schemars(rename_all = "camelCase")]`). You may find this useful if you want to change the generated schema without affecting Serde's behaviour, or if you're just not using Serde.
 
 ## Feature Flags
+- `derive` (enabled by default) - provides `#[derive(JsonSchema)]` macro
 - `impl_json_schema` - implements `JsonSchema` for Schemars types themselves
 
 ## Optional Dependencies