feat(guides): add example to goroutines (#20695)

guide/english/go/goroutines/index.md

@@ -3,16 +3,32 @@ title: Goroutines
 ---
 ## Goroutines
 
-This is a stub. [Help our community expand it](https://github.com/freecodecamp/guides/tree/master/src/pages/go/goroutines/index.md).
-
-[This quick style guide will help ensure your pull request gets accepted](https://github.com/freecodecamp/guides/blob/master/README.md).
-
-<!-- The article goes here, in GitHub-flavored Markdown. Feel free to add YouTube videos, images, and CodePen/JSBin embeds  -->
-
 Goroutines are functions or methods that run concurrently with other functions or methods. Goroutines can be thought of as light weight threads. The cost of creating a Goroutine is tiny when compared to a thread.
 
 Prefix the function or method call with the keyword `go` and you will have a new Goroutine running concurrently.
 
+Let's look at an example:
+
+    func say(s string) {
+        fmt.Println(s)
+        time.Sleep(100 * time.Millisecond)
+        fmt.Println(s)
+    }
+
+    func main() {
+        go say("hello")
+        say("world")
+    }
+    
+Output:
+
+    world
+    hello
+    hello
+    world
+    
+You can observe that since we called `say("hello")` in a goroutine, it'll run concurrently and will print the output in no particular order in regards to the regualar function call `say("world")`.
+
 #### More Information:
 * [A Tour of Go](https://tour.golang.org/concurrency/1)
 * [Go By Example](https://gobyexample.com/goroutines)