Update timesyncd.conf NTP server option (#357)

Changing the current option "Server=" to "NTP="

Source: https://man7.org/linux/man-pages/man5/timesyncd.conf.5.html

docs/prerequisite-system.md

@@ -148,7 +148,7 @@ To enable NTP you need to run the command `timedatectl set-ntp true`. You also n
 ```
 # vim /etc/systemd/timesyncd.conf
 [Time]
-Servers=0.pool.ntp.org 1.pool.ntp.org 2.pool.ntp.org 3.pool.ntp.org
+NTP=0.pool.ntp.org 1.pool.ntp.org 2.pool.ntp.org 3.pool.ntp.org
 ```
 
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