osx/*: add page for macOS interal daemons (#6705)

appsleepd
auditd
avbdevided
bird
bnepd
cfprefsd
cloudphotod
coreaudiod
distnoted
emond
filecoordinationd
launchd
notifyd
ocspd
photoanalysisd
pppd
secd
securityd
timed
universalaccessd
usernoted
vpnd

pages/osx/vpnd.md

@@ -0,0 +1,28 @@
+# vpnd
+
+> Listens for incoming VPN connections.
+> It should not be invoked manually.
+
+- Start the daemon:
+
+`vpnd`
+
+- Run the daemon in the foreground:
+
+`vpnd -x`
+
+- Run the daemon in the foreground and print logs to the terminal:
+
+`vpnd -d`
+
+- Run the daemon in the foreground, print logs to the terminal, and quit after validating arguments:
+
+`vpnd -n`
+
+- Print usage summary and exit:
+
+`vpnd -h`
+
+- Run the daemon for a specific server configuration:
+
+`vpnd -i {{server_id}}`