Fix path of Dockerfile directory

Other tutorial parts suppose that the Dockerfile is located at the same level as src folder.

language/dotnet/build-images.md

@@ -101,7 +101,7 @@ Press Ctrl+C in the terminal window to stop the application.
 
 ## Create a Dockerfile
 
-In the `dotnet-docker\src` directory, create a file named `Dockerfile`.
+In the `dotnet-docker` directory, create a file named `Dockerfile`.
 
 Next, we need to add a line in our Dockerfile that tells Docker what image
 we would like to use to build our application. Open the `Dockerfile` in an IDE or a text editor, and add the following instructions.