Add note about bytes serialization perfomance

_skeptic/Cargo.toml

@@ -18,5 +18,6 @@ serde_repr = "0.1"
 serde_test = "1.0"
 serde-transcode = "1.0"
 serde_yaml = "0.8"
+serde_bytes = "0.11"
 skeptic = "0.13"
 void = "1.0"

_src/field-attrs.md

@@ -85,6 +85,18 @@
   `$module::serialize` as the `serialize_with` function and
   `$module::deserialize` as the `deserialize_with` function.
 
+```rust
+// For some iter types custom module might significantly improve performance, 
+// for instance `Vec<u8>` ser/deserialized about 10x times faster with serde_bytes
+# use serde::{Serialize, Deserialize};
+#[derive(Serialize, Deserialize)]
+struct Fast {
+    #[serde(with = "serde_bytes")]
+    buf: Vec<u8>
+}
+# fn main() {}
+```
+
 - ##### `#[serde(borrow)]` and `#[serde(borrow = "'a + 'b + ...")]` {#borrow}
 
   Borrow data for this field from the deserializer by using zero-copy