added -- command in help

programs/zstd.1

@@ -89,6 +89,10 @@ It also features a very fast decoder, with speed > 500 MB/s per core.
 .BR \-t ", " --test
  Test the integrity of compressed files. This option is equivalent to \fB--decompress --stdout > /dev/null\fR.
  No files are created or removed.
+.TP
+.BR --
+ All arguments after -- are treated as files
+
 
 .SH DICTIONARY
 .PP

programs/zstdcli.c

@@ -144,6 +144,7 @@ static int usage_advanced(const char* programName)
     DISPLAY( "--test  : test compressed file integrity \n");
     DISPLAY( "--[no-]sparse : sparse mode (default:enabled on file, disabled on stdout)\n");
 #endif
+    DISPLAY( "--      : All arguments after \"--\" are treated as files \n");
 #ifndef ZSTD_NODICT
     DISPLAY( "\n");
     DISPLAY( "Dictionary builder :\n");