readme: add example code usage

README.md

@@ -31,6 +31,43 @@ go get -d ./...
 go run .
 ```
 
+## Examples usage of ttggame/ttgpcplayer
+
+This simple example should show, how to use an AI game engine:
+
+```golang
+package main
+
+import (
+	"fmt"
+
+	"github.com/gucio321/tic-tac-go/ttggame/ttgboard"
+	"github.com/gucio321/tic-tac-go/ttggame/ttgpcplayer"
+	"github.com/gucio321/tic-tac-go/ttggame/ttgletter"
+)
+
+func main() {
+	// create board
+	width, height := 3, 3
+	chainLen := 3
+	board := ttgboard.NewBoard(width, height, chainLen)
+
+	// fill board
+	board.SetIndexState(0, ttgletter.LetterX)
+	board.SetIndexState(4, ttgletter.LetterO)
+	board.SetIndexState(8, ttgletter.LetterX)
+	board.SetIndexState(6, ttgletter.LetterX)
+
+	fmt.Println(board)
+
+	// make move using AI engine
+	i := ttgpcplayer.GetPCMove(board, ttgletter.LetterO)
+	board.SetIndexState(i, ttgletter.LetterO)
+
+	fmt.Println(board)
+}
+```
+
 ## Screenshots
 
 ![menu](docs/menu.png)