systemd-firstboot: add page (#10493)

* systemd-firstboot: add page

---------

Co-authored-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>
Co-authored-by: Lena <126529524+acuteenvy@users.noreply.github.com>

pages/linux/systemd-firstboot.md

@@ -0,0 +1,36 @@
+# systemd-firstboot
+
+> Initialize basic system settings on or before the first boot-up of a system.
+> More information: <https://www.freedesktop.org/software/systemd/man/systemd-firstboot.html>.
+
+- Operate on the specified directory instead of the root directory of the host system:
+
+`sudo systemd-firstboot --root={{path/to/root_directory}}`
+
+- Set the system keyboard layout:
+
+`sudo systemd-firstboot --keymap={{keymap}}`
+
+- Set the system hostname:
+
+`sudo systemd-firstboot --hostname={{hostname}}`
+
+- Set the root user's password:
+
+`sudo systemd-firstboot --root-password={{password}}`
+
+- Prompt the user interactively for a specific basic setting:
+
+`sudo systemd-firstboot --prompt={{setting}}`
+
+- Force writing configuration even if the relevant files already exist:
+
+`sudo systemd-firstboot --force`
+
+- Remove all existing files that are configured by `systemd-firstboot`:
+
+`sudo systemd-firstboot --reset`
+
+- Remove the password of the system's root user:
+
+`sudo systemd-firstboot --delete-root-password`