systemd-sysusers: add page (#10693)

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

pages/linux/systemd-sysusers.md

@@ -0,0 +1,17 @@
+# systemd-sysusers
+
+> Create system users and groups.
+> If the config file is not specified, files in the `sysusers.d` directories are used.
+> More information: <https://www.freedesktop.org/software/systemd/man/systemd-sysusers.html>.
+
+- Create users and groups from a specific configuration file:
+
+`systemd-sysusers {{path/to/file}}`
+
+- Process configuration files and print what would be done without actually doing anything:
+
+`systemd-sysusers --dry-run {{path/to/file}}`
+
+- Print the contents of all config files (before each file, its name is printed as a comment):
+
+`systemd-sysusers --cat-config`