Add example for custom schema setings

docs/_includes/examples/custom_settings.rs

@@ -0,0 +1,27 @@
+use schemars::{gen::SchemaSettings, JsonSchema};
+
+#[derive(JsonSchema)]
+pub struct MyStruct {
+    pub my_int: i32,
+    pub my_bool: bool,
+    pub my_nullable_enum: Option<MyEnum>,
+}
+
+#[derive(JsonSchema)]
+pub enum MyEnum {    
+    StringNewType(String),
+    StructVariant {
+        floats: Vec<f32>,
+    }
+}
+
+fn main() {
+    let settings = SchemaSettings {
+        option_nullable: true,
+        option_add_null_type: false,
+        ..SchemaSettings::draft07()
+    };
+    let gen = settings.into_generator();
+    let schema = gen.into_root_schema_for::<MyStruct>();;
+    println!("{}", serde_json::to_string_pretty(&schema).unwrap());
+}