Merge #20152: doc: Update wallet files in files.md

defe48a51f doc: Update wallet files in files.md (Hennadii Stepanov)

Pull request description:

  This PR is a #19077 follow up, and it addresses the [comment](https://github.com/bitcoin/bitcoin/pull/19077#discussion_r504805234):

  > If need to update, there are two corrections that could be made:
  >
  >  * Line 69 "Wallets are Berkeley DB (BDB) databases" is no longer true
  >
  >  * Line 76 "Wallet lock file" should say "BDB wallet lock file"

ACKs for top commit:
  RiccardoMasutti:
    ACK defe48a
  meshcollider:
    ACK defe48a51f

Tree-SHA512: 39939f86a9c7842bf06913998305dcbd6209585f1da0fe9c274bac0572eb8464e59176884dd9e2b91312f34efad40cdeb4085ec72c2a2c1b33d16b6ab505140c

doc/files.md

@@ -8,6 +8,10 @@
 
 - [Multi-wallet environment](#multi-wallet-environment)
 
+  - [Berkeley DB database based wallets](#berkeley-db-database-based-wallets)
+
+  - [SQLite database based wallets](#sqlite-database-based-wallets)
+
 - [GUI settings](#gui-settings)
 
 - [Legacy subdirectories and files](#legacy-subdirectories-and-files)
@@ -67,26 +71,36 @@ Subdirectory       | File(s)               | Description
 
 ## Multi-wallet environment
 
-Wallets are Berkeley DB (BDB) databases:
+Wallets are Berkeley DB (BDB) or SQLite databases.
 
-Subdirectory | File(s)           | Description
--------------|-------------------|------------
-`database/`  | BDB logging files | Part of BDB environment; created at start and deleted on shutdown; a user *must keep it as safe* as personal wallet `wallet.dat`
-`./`         | `db.log`          | BDB error file
-`./`         | `wallet.dat`      | Personal wallet with keys and transactions. May be either a Berkeley DB or SQLite database file.
-`./`         | `.walletlock`     | Wallet lock file
-`./`         | `wallet.dat-journal` | SQLite Rollback Journal file for `wallet.dat`. Usually created at start and deleted on shutdown. A user *must keep it as safe* as the `wallet.dat` file.
-
-1. Each user-defined wallet named "wallet_name" resides in `wallets/wallet_name/` subdirectory.
+1. Each user-defined wallet named "wallet_name" resides in the `wallets/wallet_name/` subdirectory.
 
 2. The default (unnamed) wallet resides in `wallets/` subdirectory; if the latter does not exist, the wallet resides in the data directory.
 
-3. A wallet database path can be specified by `-wallet` option.
+3. A wallet database path can be specified with the `-wallet` option.
 
 4. `wallet.dat` files must not be shared across different node instances, as that can result in key-reuse and double-spends due the lack of synchronization between instances.
 
 5. Any copy or backup of the wallet should be done through a `backupwallet` call in order to update and lock the wallet, preventing any file corruption caused by updates during the copy.
 
+
+### Berkeley DB database based wallets
+
+Subdirectory | File(s)           | Description
+-------------|-------------------|-------------
+`database/`  | BDB logging files | Part of BDB environment; created at start and deleted on shutdown; a user *must keep it as safe* as personal wallet `wallet.dat`
+`./`         | `db.log`          | BDB error file
+`./`         | `wallet.dat`      | Personal wallet (a BDB database) with keys and transactions
+`./`         | `.walletlock`     | BDB wallet lock file
+
+### SQLite database based wallets
+
+Subdirectory | File                 | Description
+-------------|----------------------|-------------
+`./`         | `wallet.dat`         | Personal wallet (a SQLite database) with keys and transactions
+`./`         | `wallet.dat-journal` | SQLite Rollback Journal file for `wallet.dat`. Usually created at start and deleted on shutdown. A user *must keep it as safe* as the `wallet.dat` file.
+
+
 ## GUI settings
 
 `bitcoin-qt` uses [`QSettings`](https://doc.qt.io/qt-5/qsettings.html) class; this implies platform-specific [locations where application settings are stored](https://doc.qt.io/qt-5/qsettings.html#locations-where-application-settings-are-stored).