Add documentation for the mithril-common::protocol module

mithril-common/src/protocol/mod.rs

@@ -1,4 +1,8 @@
-//! Todo: module doc
+//! Protocol module
+//!
+//! This module contains types that standardize and make easier mithril protocol operations
+//! such as issuing single signatures, aggregating them as multi-signatures or computing
+//! aggregate verification keys.
 
 mod multi_signer;
 mod signer_builder;