slock.1: use standard wording for options

Remove the OPTIONS section and add an EXIT STATUS section.

slock.1

@@ -14,11 +14,14 @@ is a simple X screen locker.
 If provided,
 .Ar cmd
 is executed after the screen has been locked.
-.Sh OPTIONS
+.Pp
+The options are as follows:
 .Bl -tag -width Ds
 .It Fl v
 Print version information to stdout and exit.
 .El
+.Sh EXIT STATUS
+.Ex -std
 .Sh EXAMPLES
 $
 .Nm