Improve getting started example

README.md

@@ -57,7 +57,7 @@ go get github.com/blushft/go-diagrams
 Create a diagram:
 
 ```golang
-d, err := diagram.New(diagram.Label("my-diagram"), diagram.Filename("diagram"))
+d, err := diagram.New(diagram.Label("my-diagram"), diagram.Filename("diagram-example"))
 if err != nil {
     log.Fatal(err)
 }
@@ -81,5 +81,6 @@ Go-Diagrams will create a folder in the current working directory with the graph
 Create an ouput image with any graphviz compatible renderer:
 
 ```sh
-dot -Tpng diagram.dot > diagram.png
+./diagram-example
+dot -Tpng go-diagrams/go-diagram.dot > diagram-example.png
 ```