Add example for remote deriving JsonSchema

docs/_includes/examples/remote_derive.rs

@@ -0,0 +1,38 @@
+// Pretend that this is somebody else's crate, not a module.
+mod other_crate {
+    // Neither Schemars nor the other crate provides a JsonSchema impl  
+    // for this struct.
+    pub struct Duration {
+        pub secs: i64,
+        pub nanos: i32,
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+use other_crate::Duration;
+use schemars::{schema_for, JsonSchema};
+
+// This is just a copy of the remote data structure that Schemars can use to
+// create a suitable JsonSchema impl.
+#[derive(JsonSchema)]
+pub struct DurationDef {
+    pub secs: i64,
+    pub nanos: i32,
+}
+
+// Now the remote type can be used almost like it had its own JsonSchema impl
+// all along. The `with` attribute gives the path to the definition for the
+// remote type. Note that the real type of the field is the remote type, not
+// the definition type.
+#[derive(JsonSchema)]
+pub struct Process {
+    pub command_line: String,
+    #[serde(with = "DurationDef")]
+    pub wall_time: Duration,
+}
+
+fn main() {
+    let schema = schema_for!(Process);
+    println!("{}", serde_json::to_string_pretty(&schema).unwrap());
+}