podman.service: set doc to podman-system-service

podman-api(1) does not exist, so set the man page to
podman-system-service(1).  Same for the .socket.

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

contrib/systemd/system/podman.service

@@ -2,7 +2,7 @@
 Description=Podman API Service
 Requires=podman.socket
 After=podman.socket
-Documentation=man:podman-api(1)
+Documentation=man:podman-system-service(1)
 StartLimitIntervalSec=0
 
 [Service]

contrib/systemd/system/podman.socket

@@ -1,6 +1,6 @@
 [Unit]
 Description=Podman API Socket
-Documentation=man:podman-api(1)
+Documentation=man:podman-system-service(1)
 
 [Socket]
 ListenStream=%t/podman/podman.sock