xbps-uunshare: document end of options argument

Signed-off-by: Doan Tran Cong Danh <congdanhqx@gmail.com>

bin/xbps-uunshare/main.c

@@ -76,7 +76,7 @@ die(const char *fmt, ...)
 static void __attribute__((noreturn))
 usage(const char *p)
 {
-	printf("Usage: %s [-b src:dest] <dir> <cmd> [<cmdargs>]\n\n"
+	printf("Usage: %s [-b src:dest] [--] <dir> <cmd> [<cmdargs>]\n\n"
 	    "-b src:dest Bind mounts <src> into <dir>/<dest> (may be specified multiple times)\n\n", p);
 	exit(EXIT_FAILURE);
 }

bin/xbps-uunshare/xbps-uunshare.1

@@ -37,6 +37,12 @@ Please note that both
 and
 .Ar dest
 must be absolute paths and must exist.
+.It Fl -
+Stop interpreting following arguments as options.
+This option is useful if some of
+.Ar ARGS
+are options passed to
+.Ar COMMAND .
 .El
 .Sh NOTES
 The