Document the impl_protocol macro

Author: GabrielMajeri

src/proto/macros.rs

@@ -1,5 +1,20 @@
 /// Implements the `Protocol` trait for a type.
 /// Also marks the type as not sync and not send.
+///
+/// # Usage
+///
+/// ```rust
+/// struct CustomProtocol {
+///     function_pointer: extern "C" fn() -> (),
+///     data: usize
+/// }
+///
+/// impl_proto! {
+///     protocol CustomProtocol {
+///         GUID = 0x1234_5678, 0x9ABC 0xDEF0, [0x12, 0x23, 0x34, 0x45, 0x56, 0x67, 0x78, 0x89];
+///     }
+/// }
+/// ```
 macro_rules! impl_proto {
     (
         protocol $p:ident {