Revise docs.

doc/src/rust/serde.md

@@ -105,6 +105,17 @@ let x: MyStruct = from_dynamic(&result)?;
 ```
 
 
+Cannot Deserialize Shared Values
+-------------------------------
+
+A [`Dynamic`] containing a _shared_ value cannot be deserialized - i.e. it will give a type error.
+
+Use `Dynamic::flatten` to obtain a cloned copy before deserialization
+(if the value is not shared, it is simply returned and not cloned).
+
+Shared values are turned off via the [`no_closure`] feature.
+
+
 Lighter Alternative
 -------------------