systemd-run: add page (#9949)

* systemd-run: add page

* systemd-run: fix minor typo

* systemd-run: reorder wording to reduce ambiguity

* systemd-run: apply review suggestions

Co-authored-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>

---------

Co-authored-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>

pages/linux/systemd-run.md

@@ -0,0 +1,24 @@
+# systemd-run
+
+> Run programs in transient units.
+> More information: <https://manned.org/systemd-run>.
+
+- Start a transient service:
+
+`sudo systemd-run {{command}} {{argument1 argument2 ...}}`
+
+- Start a transient service under the service manager of the current user (no privileges):
+
+`systemd-run --user {{command}} {{argument1 argument2 ...}}`
+
+- Start a transient service with a custom unit name and description:
+
+`sudo systemd-run --unit={{name}} --description={{string}} {{command}} {{argument1 argument2 ...}}`
+
+- Start a transient service that does not get cleaned up after it terminates with a custom environment variable:
+
+`sudo systemd-run --remain-after-exit --set-env={{name}}={{value}} {{command}} {{argument1 argument2 ...}}`
+
+- Start a transient timer that periodically runs its transient service (see `man systemd.time` for calendar event format):
+
+`sudo systemd-run --on-calendar={{calendar_event}} {{command}} {{argument1 argument2 ...}}`