CH02::constructing: clarify offline requirements

Previous text said that wallets can construct tranactions offline.  Add
clarification that this requires the wallet to already know what inputs
it controls.

ch02.asciidoc

@@ -329,11 +329,12 @@ image::images/mbc2_0207.png["Distributing Transaction"]
 
 ((("transactions", "constructing", id="Tconstruct02")))((("wallets",
 "constructing transactions")))Alice's wallet application contains all
-the logic for selecting appropriate inputs and outputs to build a
-transaction to Alice's specification. Alice only needs to specify a
-destination and an amount, and the rest happens in the wallet
-application without her seeing the details. Importantly, a wallet
-application can construct transactions even if it is completely offline.
+the logic for selecting inputs and generating outputs to build a
+transaction to Alice's specification. Alice only needs to choose a
+destination, amount, and transaction fee, and the rest happens in the wallet
+application without her seeing the details. Importantly, if a wallet
+already knows what inputs it controls, it can construct transactions
+even if it is completely offline.
 Like writing a check at home and later sending it to the bank in an
 envelope, the transaction does not need to be constructed and signed
 while connected to the Bitcoin network.