Fix typo and improve formatting in #[pyo3(transparent)] field conversion documentation

Author: Cheukting

guide/src/conversions/traits.md

@@ -697,8 +697,7 @@ struct RustyStruct {
 # }
 ```
 
-This tries to convert a mapping with the key `"key"`.
-The `item` can take any valid literal.
+This tries to convert a mapping with the key `"key"`. The `item` can take any valid literal.
 
 For structs with a single field (newtype pattern) the `#[pyo3(transparent)]` option can be used to forward the implementation to the inner type.