CH01::Backups: s/mnemonic/recovery code/, add detail and warnings

- Use "recovery code" instead of "mnemonic phrase" or "seed phrase".  A
  new tipbox describes that mnemonic implies memorization but that's bad
  practice.  The phrase recovery code is generic enough to apply to a
  variety of schemes, including Electrum seed words, BIP38 seed words,
  aezeed, and non-phrase schemes like that used in Muun.

- Be clearer about the difference between "wallet" and "wallet
  software".

- Mention that restoring from a code doesn't restore labels or
  offchain transaction info.

- Warn about re-entering your code into malware / phishing attacks.

ch01.asciidoc

@@ -319,36 +319,87 @@ the option to create a new Bitcoin wallet. Because the wallet she has
 chosen is a non-custodial wallet, Alice (and only Alice) will be in
 control of her keys. Therefore, she bears responsibility for backing
 them up, since losing the keys means she loses access to the bitcoin. To
-facilitate this, her wallet produces a _mnemonic phrase_ (explained more
-in <<mnemonic_phrase_intro>>), in the form of 12 English words that can
-be used to restore her wallet on any of the hundreds of compatible
-software or hardware wallets.
-
-Let's elaborate a bit on the mnemonic phrase, next.
-
-[[mnemonic_phrase_intro]]
-==== Mnemonic Phrase
-
-Most modern non-custodial Bitcoin wallets will provide a _mnemonic
-phrase_ (also sometimes called a "seed" or "seed phrase") for their user
-to back up. The mnemonic phrase usually consists of 12 English words,
-selected randomly by the software, and used as the basis for the keys
-that are generated by the wallet. A sample mnemonic phrase is shown in
-<<mnemonic_phrase_sample>>.
-
-[[mnemonic_phrase_sample]]
-.Alice is shown a 12-word mnemonic phrase that she must backup (offline on paper)
-image::images/mnemonic_phrase_sample.png[".Alice is shown a 12-word mnemonic phrase that she must backup (offline on paper)"]
-
-This mnemonic phrase can be used by Alice to restore *all* the
-transactions and funds in her wallet in the case of an event such as a
-lost mobile device, a software bug, or memory corruption. The mnemonic
-phrase is based on a common standard and therefore can be restored on
-any compatible software or hardware wallet. This allows Alice to try
-different wallets and also removes any dependency on the software or
-hardware maker of the wallet.
-
-Of note, when receiving funds to a new mobile wallet for the first time, many wallets will often re-verify that you have securely backed-up your mnemonic phrase. This can range from a simple prompt to requiring the user to manually re-enter the phrase.
+facilitate this, her wallet produces a _recovery code_ (explained more in
+<<recovery_code_intro>>) that can be used
+to restore her wallet.
+
+Let's elaborate a bit on the recovery code, next.
+
+[[recovery_code_intro]]
+==== Recovery Code
+
+Most modern non-custodial Bitcoin wallets will provide a _recovery
+code_ for their user
+to back up.  The recovery code usually consists of numbers, letters, or words
+selected randomly by the software, and is used as the basis for the keys
+that are generated by the wallet. Sample recovery codes from different wallets are shown in
+<<recovery_code_sample>>.
+
+[[recovery_code_sample]]
+[cols="1,1"]
+|===
+| Wallet | Recovery code
+
+| BlueWallet
+| (1) media (2) suspect (3) effort (4) dish (5) album (6) shaft (7) price (8) junk (9) pizza (10) situate (11) oyster (12) rib
+
+| Electrum
+| nephew dog crane clever quantum crazy purse traffic repeat fruit old clutch
+
+| Muun
+| LAFV TZUN V27E NU4D WPF4 BRJ4 ELLP BNFL
+|===
+
+[TIP]
+====
+A recovery code phrase is sometimes called a "mnemonic" or "mnemonic phrase",
+which implies you should memorize the phrase, but writing the phrase
+down on paper takes less work and tends to be more reliable than most
+people's memories.  Another alternative name is "seed phrase" because
+it provides the input ("seed") to the function which generates all of
+a wallet's keys.
+====
+
+If something happens to Alice's wallet, she can download a new copy of
+her wallet software and enter this recovery code to rebuild the wallet
+database of all the onchain transactions she's ever sent or received.
+However, recovering from the recovery code will not by itself restore any additional
+data Alice entered into her wallet, such as the names she associated
+with particular addresses or transactions.  Although losing access to
+that metadata isn't as important as losing access to money, it can
+still be important in its own way.  Imagine you need to review an old
+bank or credit card statement and the name of every entity you paid (or
+who paid you) has been blanked out.  To prevent losing metadata, many
+wallets provide an additional backup feature beyond recovery codes.
+
+For some wallets, that additional backup feature is even more important
+today than it used to be.  Many Bitcoin payments are now made using
+_offchain_ technology, where not every payment is stored in the public block
+chain.  This reduces users costs and improves privacy, among other
+benefits, but it means that a mechanism like recovery codes that depends on
+onchain data can't guarantee recovery of all of a user's bitcoins.  For
+applications with offchain support, it's important to make frequent
+backups of the wallet database.
+
+Of note, when receiving funds to a new mobile wallet for the first time,
+many wallets will often re-verify that you have securely backed-up your
+recovery code. This can range from a simple prompt to requiring the
+user to manually re-enter the code.
+
+[WARNING]
+====
+Although many legitimate wallets will prompt their user to re-enter
+your recovery code, there are also many malware applications that mimic the
+design of a wallet, insist you enter your recovery code, and then
+relay any entered phrases to the malware developer so they can steal
+your funds.  This is the equivilent of phishing websites that try to
+trick you into giving them your bank passphrase.  For most wallet
+applications, the only times they will ask for your recovery code are during
+the initial set up (before you have received any bitcoins) and during
+recovery (after you lost access to your original wallet).  If the application
+asks for your recovery code any other time, consult with an expert to
+ensure you aren't being phished.
+====
 
 ==== Running the wallet application