fix misleading assert messages && add some comments

agora-sample/Sample/Proposal.hs

@@ -374,6 +374,10 @@ voteOnProposal params =
       stakeOutput =
         stakeInput
           { txOutDatumHash = Just $ toDatumHash stakeOutputDatum
+          -- We won't include the minimum Ada in the output value
+          -- due to how we check the output value in the stake validator.
+          -- The implementation is correct though, it should work in a
+          -- real on-chain environment.
           }
 
       ---