c# core: Add documentation for untagged bonded.

cs/src/core/protocols/SimpleBinary.cs

@@ -53,6 +53,13 @@
 
                             key, mapped     each item encoded according to its type
 
+                                           .-------. .-----------.
+                    bonded                 | count | | marshaled |
+                                           '-------' '-----------'
+                            count           uint32 count of bytes (always fixed-width, even in v2)
+
+                            marshaled       a marshaled payload
+
 */
 #endregion