[guides] refs fibercrypto#130 - Document hardware wallet contract

content/dev-docs/guides/v2.wallet.md

@@ -41,5 +41,18 @@ To increase security, private keys can be generated and stored by a separate wal
 
 Signing-only wallets programs typically use deterministic key creation (described in a later subsection) to create parent private and public keys which can create child private and public keys. At first, the signing-only wallet creates a parent private key and transfers the corresponding parent public key to the networked wallet. The later does the rest. Often, users are given a chance to review the unsigned transactions’ details (particularly the output details) using the signing-only wallet. After the optional review step, the signing-only wallet uses the parent private key to derive the appropriate child private keys and signs the transactions, giving the signed transactions back to the PEX for subsequent broadcast.
 
+##### Hardware Wallets
 
+Hardware wallets are devices dedicated to running a signing-only wallet. Their dedication lets them eliminate many of the vulnerabilities present in operating systems designed for general use, allowing them to safely communicate directly with other devices so users don’t need to transfer data manually.
+
+The user’s workflow is defined by `HardwareWallet` contract and looks something like:
+
+1. (Hardware) Create parent private and public keys. Connect hardware wallet to a networked device so it can get the parent public key.
+2. (Networked) As you would with a full-service wallet, distribute public keys to receive payment. When ready to spend coins, fill in the transaction details, connect the hardware wallet, and start spending workflow. The networked wallet will automatically send the transaction details to the hardware wallet.
+3. (Hardware) Review the transaction details on the hardware wallet’s screen. Some hardware wallets may prompt for a passphrase or PIN number. The hardware wallet signs the transaction and uploads it to the networked wallet.
+4. (Networked) The networked wallet receives the signed transaction from the hardware wallet and broadcasts it to the network.
+
+The primary advantage of hardware wallets is their possibility for greatly improved security over full-service wallets with much less hassle than offline wallets.
+
+The primary disadvantage of hardware wallets is their hassle. Even though the hassle is less than that of offline wallets, the user must still purchase a hardware wallet device and carry it with them whenever they need to make a transaction using the signing-only wallet.