>> add replace flag to help message

> fix whitespace issues in help message

main.go

@@ -362,6 +362,9 @@ func printHelp() {
      Select a set of characters to limit filenames to.
    -p,--portable
      Alias for "--valid-set posix"
+   -c,--replace TARGET:REPLACEMENT1,REPLACEMENT2,...
+     Replace each instance of TARGET in file names with REPLACEMENT1 the 
+     first time they appear, REPLACEMENT2 the second time, and so on
 
  See man page for more details
 `);