;doc: update command docs

hledger/Hledger/Cli/Commands/Stats.txt

@@ -3,6 +3,7 @@ stats
 Show journal and performance statistics.
 
 Flags:
+  -1                        show a single line of output
   -v --verbose              show more detailed output
   -o --output-file=FILE     write output to FILE.
 
@@ -10,20 +11,24 @@ The stats command shows summary information for the whole journal, or a
 matched part of it. With a reporting interval, it shows a report for
 each report period.
 
-The default output is fairly impersonal, though it reveals the main file
-name. With -v/--verbose, more details are shown, like file paths,
-included files, and commodity names.
+It also shows some performance statistics:
 
-It also shows some run time statistics:
+- how long the program ran for
+- the number of transactions processed per second
+- the peak live memory in use by the program to do its work
+- the peak allocated memory as seen by the program
 
-- elapsed time
-- throughput: the number of transactions processed per second
-- live: the peak memory in use by the program to do its work
-- alloc: the peak memory allocation from the OS as seen by GHC.
-  Measuring this externally, eg with GNU time, is more accurate; usually
-  that will be a larger number; sometimes (with swapping?) smaller.
+By default, the output is reasonably discreet; it reveals the main file
+name, your activity level, and the speed of your machine.
 
-The stats command's run time is similar to that of a balance report.
+With -v/--verbose, more details are shown: the full paths of all files,
+and the names of the commodities you work with.
+
+With -1, only one line of output is shown, in a machine-friendly
+tab-separated format: the program version, the main journal file name,
+and the performance stats,
+
+The run time of stats is similar to that of a balance report.
 
 Example:
 
@@ -41,5 +46,8 @@ Commodities         : 26
 Market prices       : 1000
 Runtime stats       : 0.12 s elapsed, 8266 txns/s, 4 MB live, 16 MB alloc
 
+$ hledger stats -1 -f examples/10ktxns-1kaccts.journal
+1.50.99-g0835a2485-20251119, mac-aarch64    10ktxns-1kaccts.journal 0.66 s elapsed  15244 txns/s    28 MB live  86 MB alloc
+
 This command supports the -o/--output-file option (but not
 -O/--output-format).