biff: add page (#16485)

* biff: add page

---------

Co-authored-by: Managor <42655600+Managor@users.noreply.github.com>
Co-authored-by: Fazle Arefin <fazlearefin@users.noreply.github.com>

pages/common/biff.md

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+# biff
+
+> A simple utility for doing datetime arithmetic, parsing and formatting.
+> More information: <https://github.com/burntsushi/biff>.
+
+- Print the current time in a format of your choosing:
+
+`biff time fmt {{[-f|--format]}} rfc3339 now`
+
+- Print multiple relative times in one command:
+
+`biff time fmt {{[-f|--format]}} '%c' now -1d 'next sat' 'last monday' '9pm last mon'`
+
+- Print the current time in another time zone, and round it the nearest 15 minute increment:
+
+`biff time in Asia/Bangkok now | biff time round {{[-i|--increment]}} 15 {{[-s|--smallest]}} minute`
+
+- Convert a time between two different time zone:
+
+`TZ='Japan' biff time in America/New_York 02:30`
+
+- Print a past or future time relative to current time:
+
+`biff time add {{-1d|1d|1w|-1m|1y|...}} now`
+
+- Add a complex duration to the current time:
+
+`biff time add '1 week, 12 hours ago' now`
+
+- Find the duration since a date in the past and round it to the desired precision:
+
+`biff span since 2025-01-20T12:00 {{[-l|--largest]}} year`
+
+- Find timestamps in a log file and reformat them into your local time in place:
+
+`biff tag lines /tmp/access.log | biff time in system | biff time fmt {{[-f|--format]}} '%c' | head {{[-n|--lines]}} 3 | biff untag {{[-s|--substitute]}}`