docs: add -s/--since of uptime to extensions

[cakebaker]

No description provided.

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/tail/inotify-dir-recreate (passes in this run but fails in the 'main' branch)

[sylvestre]

Fun, on Debian:

$ LANG=C /usr/bin/uptime --version
uptime from procps-ng 4.0.4
$  /usr/bin/uptime -s
2024-05-01 13:50:56

With the coreutils:

$ LANG=C ./uptime -s
./uptime: invalid option -- 's'

[cakebaker]

Another option is to remove -s/--since here in the coreutils version of uptime and move it to the (not yet existing) procps version as I think we have to implement uptime twice anyway due to their different behavior:

// proc-ps
$ LANG=C /usr/bin/uptime
 07:04:57 up 34 min,  1 user,  load average: 0.14, 0.27, 0.58
// GNU coreutils
$ LANG=C ./projects/gnu/src/uptime
 07:05:02  up   0:34,  5 users,  load average: 0.13, 0.27, 0.57

[tertsdiepraam]

That different number of users is really surprising...

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/inotify-dir-recreate (fails in this run but passes in the 'main' branch)