Update the readme with -rm and -version flags

[gabrielbussolo]

closes #188 showing the new usage:

moq [flags] source-dir interface [interface2 [interface3 [...]]]
  -fmt string
    	go pretty-printer: gofmt, goimports or noop (default gofmt)
  -out string
    	output file (default stdout)
  -pkg string
    	package name (default will infer)
  -rm
    	first remove output file, if it exists
  -skip-ensure
    	suppress mock implementation check, avoid import cycle if mocks generated outside of the tested package
  -stub
    	return zero values when no mock implementation is provided, do not panic
  -version
    	show the version for moq
Specifying an alias for the mock is also supported with the format 'interface:alias'
Ex: moq -pkg different . MyInterface:MyMock

Signed-off-by: Gabriel Bussolo gabreeiel@gmail.com

[matryer]

Thank you :)