add vendor & update README.md

vendor/github.com/mattn/go-isatty/isatty_linux.go

@@ -0,0 +1,18 @@
+// +build linux
+// +build !appengine,!ppc64,!ppc64le
+
+package isatty
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+const ioctlReadTermios = syscall.TCGETS
+
+// IsTerminal return true if the file descriptor is terminal.
+func IsTerminal(fd uintptr) bool {
+	var termios syscall.Termios
+	_, _, err := syscall.Syscall6(syscall.SYS_IOCTL, fd, ioctlReadTermios, uintptr(unsafe.Pointer(&termios)), 0, 0, 0)
+	return err == 0
+}