How to add pause to a Go program?

You can pause the program for an arbitrarily long time by using time.Sleep(). For example:

package main
import ( "fmt"
         "time"
       )   

func main() {
  fmt.Println("Hello world!")
  duration := time.Second
  time.Sleep(duration)
}

To increase the duration arbitrarily you can do:

duration := time.Duration(10)*time.Second // Pause for 10 seconds

EDIT: Since the OP added additional constraints to the question the answer above no longer fits the bill. You can pause until the Enter key is pressed by creating a new buffer reader which waits to read the newline (\n) character.

package main
import ( "fmt"
         "bufio"
         "os"
       )

func main() {
  fmt.Println("Hello world!")
  fmt.Print("Press 'Enter' to continue...")
  bufio.NewReader(os.Stdin).ReadBytes('\n') 
}