chore: add note to pack arguments (#5304)

aztec/src/oracle/arguments.nr

@@ -1,7 +1,11 @@
 #[oracle(packArguments)]
 fn pack_arguments_oracle<N>(_args: [Field; N]) -> Field {}
 
-// TODO: explain what this does.
+/// - Pack arguments will notify the simulator that these arguments will be used later at
+///   some point in the call. 
+/// - When the external call is made later, the simulator will know what the values unpack to.
+/// - This oracle will not be required in public vm functions, as the vm will keep track of arguments 
+///   itself.
 unconstrained pub fn pack_arguments<N>(args: [Field; N]) -> Field {
     pack_arguments_oracle(args)
 }