Improve time zone document (#714)

- Move from Common Tasks to Configuration Guides, since most users will
  just use the GUI

- Rename from `change-timezone-terminal.md` to `change-time-zone.md`
  (1) because we don't want multiple time zone documents for terminal
  and non-terminal usage and (2) to make the orthography of "time zone"
  consistent; update title and permalink accordingly

- Make heading syntax consistent

- Add heading

- Fix code block syntax

- Fix typo

- Add page to ToC

configuration/change-time-zone.md

@@ -1,14 +1,15 @@
 ---
 layout: doc
-title: Change Time Zone in Terminal
-permalink: /doc/change-timezone-terminal/
+title: Changing your Time Zone
+permalink: /doc/change-time-zone/
 ---
 
-Change Time Zone in Terminal
-============================
+# Changing your Time Zone #
 
 ## Qubes 4.0 ##
 
+### Command line ###
+
 If you use the i3 window manager or would prefer to change the system's time
 zone in terminal you can issue the `timedatectl` command with the option
 `set-timezone`.
@@ -16,9 +17,7 @@ zone in terminal you can issue the `timedatectl` command with the option
 For example, to set the system's time zone to Berlin, Germany type in a dom0
 terminal:
 
-   ~~~~
-   $ sudo timedatectl set-timezone 'Europe/Berlin
-   ~~~~
+    $ sudo timedatectl set-timezone 'Europe/Berlin'
 
 You can list the available time zones with the option `list-timezones` and show
 the current settings of the system clock and time zone with option `status`.
@@ -26,14 +25,12 @@ the current settings of the system clock and time zone with option `status`.
 Example output status of `timedatectl` on a system with time zone set to
 Europe/Berlin:
 
-   ~~~~
-   [user@dom0 ~]$ timedatectl status
-         Local time: Sun 2018-10-14 06:20:00 CEST
-     Universal time: Sun 2018-10-14 04:20:00 UTC
-           RTC time: Sun 2018-10-14 04:20:00
-          Time zone: Europe/Berlin (CEST, +0200)
-    Network time on: no
-   NTP synchronized: no
-    RTC in local TZ: no
-   ~~~~
+    [user@dom0 ~]$ timedatectl status
+          Local time: Sun 2018-10-14 06:20:00 CEST
+      Universal time: Sun 2018-10-14 04:20:00 UTC
+            RTC time: Sun 2018-10-14 04:20:00
+           Time zone: Europe/Berlin (CEST, +0200)
+     Network time on: no
+    NTP synchronized: no
+     RTC in local TZ: no
 

doc.md

@@ -127,6 +127,7 @@ Configuration Guides
  * [Multibooting](/doc/multiboot/)
  * [Resize Disk Image](/doc/resize-disk-image/)
  * [RPC Policies](/doc/rpc-policy/)
+ * [Changing your Time Zone](/doc/change-time-zone)
  * [Installing ZFS in Qubes](/doc/zfs/)
  * [Mutt Guide](/doc/mutt/)
  * [Postfix Guide](/doc/postfix/)