Merge #20076: doc: Update and improve files.md

2dc79c4 doc: Update and improve files.md (Hennadii Stepanov)

Pull request description:

  This PR adds to the `files.md`:
  - the `signet` subdirectory
  - the `ip_asn.map` file
  - some small improvements

ACKs for top commit:
  practicalswift:
    ACK 2dc79c4
  MarcoFalke:
    ACK 2dc79c4

Tree-SHA512: f645486a26293e91eda826dee46e5798af9a81be410d48d07c2714f416da19b85e7e75b1a638b0e03a3e6dc486a8bb65c4be811eb2ff51b66f5817aecf89416d

Author: fanquake

doc/files.md

@@ -26,15 +26,16 @@ Linux    | `$HOME/.bitcoin/`
 macOS    | `$HOME/Library/Application Support/Bitcoin/`
 Windows  | `%APPDATA%\Bitcoin\` <sup>[\[1\]](#note1)</sup>
 
-2. The non-default data directory path can be specified by `-datadir` option.
+2. A custom data directory path can be specified with the `-datadir` option.
 
 3. All content of the data directory, except for `bitcoin.conf` file, is chain-specific. This means the actual data directory paths for non-mainnet cases differ:
 
-Chain option        | Data directory path
---------------------|--------------------
-no option (mainnet) | *path_to_datadir*`/`
-`-testnet`          | *path_to_datadir*`/testnet3/`
-`-regtest`          | *path_to_datadir*`/regtest/`
+Chain option                   | Data directory path
+-------------------------------|------------------------------
+`-chain=main` (default)        | *path_to_datadir*`/`
+`-chain=test` or `-testnet`    | *path_to_datadir*`/testnet3/`
+`-chain=signet` or `-signet`   | *path_to_datadir*`/signet/`
+`-chain=regtest` or `-regtest` | *path_to_datadir*`/regtest/`
 
 ## Data directory layout
 
@@ -44,17 +45,18 @@ Subdirectory       | File(s)               | Description
 `blocks/index/`    | LevelDB database      | Block index; `-blocksdir` option does not affect this path
 `blocks/`          | `blkNNNNN.dat`<sup>[\[2\]](#note2)</sup> | Actual Bitcoin blocks (in network format, dumped in raw on disk, 128 MiB per file)
 `blocks/`          | `revNNNNN.dat`<sup>[\[2\]](#note2)</sup> | Block undo data (custom format)
-`chainstate/`      | LevelDB database      | Blockchain state (a compact representation of all currently unspent transaction outputs and some metadata about the transactions they are from)
+`chainstate/`      | LevelDB database      | Blockchain state (a compact representation of all currently unspent transaction outputs (UTXOs) and metadata about the transactions they are from)
 `indexes/txindex/` | LevelDB database      | Transaction index; *optional*, used if `-txindex=1`
 `indexes/blockfilter/basic/db/` | LevelDB database      | Blockfilter index LevelDB database for the basic filtertype; *optional*, used if `-blockfilterindex=basic`
 `indexes/blockfilter/basic/`    | `fltrNNNNN.dat`<sup>[\[2\]](#note2)</sup> | Blockfilter index filters for the basic filtertype; *optional*, used if `-blockfilterindex=basic`
-`wallets/`         |                       | [Contains wallets](#multi-wallet-environment); can be specified by `-walletdir` option; if `wallets/` subdirectory does not exist, a wallet resides in the data directory
+`wallets/`         |                       | [Contains wallets](#multi-wallet-environment); can be specified by `-walletdir` option; if `wallets/` subdirectory does not exist, wallets reside in the [data directory](#data-directory-location)
 `./`               | `banlist.dat`         | Stores the IPs/subnets of banned nodes
 `./`               | `bitcoin.conf`        | User-defined [configuration settings](bitcoin-conf.md) for `bitcoind` or `bitcoin-qt`. File is not written to by the software and must be created manually. Path can be specified by `-conf` option
 `./`               | `bitcoind.pid`        | Stores the process ID (PID) of `bitcoind` or `bitcoin-qt` while running; created at start and deleted on shutdown; can be specified by `-pid` option
 `./`               | `debug.log`           | Contains debug information and general logging generated by `bitcoind` or `bitcoin-qt`; can be specified by `-debuglogfile` option
 `./`               | `fee_estimates.dat`   | Stores statistics used to estimate minimum transaction fees and priorities required for confirmation
 `./`               | `guisettings.ini.bak` | Backup of former [GUI settings](#gui-settings) after `-resetguisettings` option is used
+`./`               | `ip_asn.map`          | IP addresses to Autonomous System Numbers (ASNs) mapping used for bucketing of the peers; path can be specified with the `-asmap` option
 `./`               | `mempool.dat`         | Dump of the mempool's transactions
 `./`               | `onion_private_key`   | Cached Tor onion service private key for `-listenonion` option
 `./`               | `peers.dat`           | Peer IP address database (custom format)
@@ -101,7 +103,6 @@ Path           | Description | Repository notes
 
 ## Notes
 
-<a name="note1">1</a>. The `/` (slash, U+002F) is used as the platform-independent path component separator in this paper.
+<a name="note1">1</a>. The `/` (slash, U+002F) is used as the platform-independent path component separator in this document.
 
 <a name="note2">2</a>. `NNNNN` matches `[0-9]{5}` regex.
-