Improve description of signalproxy objects

docs/protocol/serialization/primitive_objects.md

@@ -7,6 +7,25 @@ Serialization of basic types is trivial and will not be discussed here.
 Primitive types are serialized by serializing each of their fields
 sequentially. 
 
+## Type Aliases
+
+Certain types have a representation which is identical to a pre-existing type
+in this document. For this reason, we do not define them twice, but list the
+type whose network representation they borrow here:
+
+|Type name      | Network representation |
+|-------------- | ---------------------- |
+|BufferId       | `Int`                  |
+|IdentityId     | `Int`                  |
+|NetworkId      | `Int`                  |
+|MsgId          | `Long`                 |
+|PeerPtr        | `Long`                 |
+|IrcUser        | `QVariantMap`          |
+|IrcChannel     | `QVariantMap`          |
+|Identity       | `QVariantMap`          |
+|NetworkInfo    | `QVariantMap`          |
+|Network::Server| `QVariantMap`          |
+
 ## String
 
 Strings are serialized as a signed int of the length in bytes plus their content