fix: doc: Recommend system timezone in UTC

Closes: #40090
11 jobs for m12 in 9 minutes and 23 seconds (queued for 6 seconds)
Status Job ID Name Coverage
  Test
passed python310 #26679

00:07:30

passed python36 #26671

00:08:08

passed python37tor035 #26672

00:08:01

passed python37tor045 #26673

00:08:42

passed python37tor046 #26674

00:07:41

passed python37tormaster #26675

00:08:36

passed python37torstable #26676

00:07:04

passed python38 #26677

00:04:47

passed python39 #26678

00:07:46

 
  Deploy
passed pages #26680

00:00:40

passed pages:deploy

00:00:00