add readme entries for new image examples

Author: SimonWaldherr

expert/image3.go

@@ -103,6 +103,6 @@ func main() {
 
 	err = png.Encode(file, img)
 	if err != nil {
-	    log.Fatalf("Error encoding image: %s\n", err)
+		log.Fatalf("Error encoding image: %s\n", err)
 	}
 }

readme.md

@@ -451,6 +451,18 @@ Convert a image to a grayscale and to a color inverted image
 go run image.go
 ```
 
+Generate an image with three colored circles (with intersection)
+
+```Shell
+go run image2.go
+```
+
+Generate an image representing the Mandelbrot fractal
+
+```Shell
+go run image3.go
+```
+
 Sql (sqlite) golang example
 
 ```Shell