describe custom de/ser-ializer

README.md

@@ -19,3 +19,25 @@ This library will support XML de/ser-ializing with all specific features.
 - [x] **attribute**: this field is defined as an attribute
 - [x] **text**: this field match to the text content
 - [ ] **namespace**: defines the namespace of the field
+
+## Custom De/Ser-rializer
+
+Any type can define a custom deserializer and/or serializer.
+To implement it, define the implementation of YaDeserialize/YaSerialize
+
+```rust
+impl YaDeserialize for MyType {
+  fn deserialize<R: Read>(reader: &mut yaserde::de::Deserializer<R>) -> Result<Self, String> {
+    // deserializer code
+  }
+}
+```
+
+```rust
+
+impl YaSerialize for MyType {
+  fn serialize<W: Write>(&self, writer: &mut yaserde::ser::Serializer<W>) -> Result<(), String> {
+    // serializer code
+  }
+}
+```