add link to the visual testing blog post

Author: bahmutov

README.md

@@ -285,7 +285,7 @@ If you are using [plugins/cra-v3](plugins/cra-v3) it instruments the code on the
 
 You can use any Cypress [Visual Testing plugin](https://on.cypress.io/plugins#visual-testing) to perform [visual testing](https://on.cypress.io/visual-testing) from the component tests. This repo has several example projects, see [visual-sudoku](examples/visual-sudoku), [visual-testing-with-percy](examples/visual-testing-with-percy), [visual-testing-with-happo](examples/visual-testing-with-happo), and [visual-testing-with-applitools](examples/visual-testing-with-applitools).
 
-For a larger Do-It-Yourself example with an hour long list of explanation videos, see [bahmutov/sudoku](https://github.com/bahmutov/sudoku) repository. There you can also find an example of testing responsive design, as shown in this [video](https://youtu.be/j8yV3uKIJO0).
+For a larger Do-It-Yourself example with an hour long list of explanation videos, see [bahmutov/sudoku](https://github.com/bahmutov/sudoku) repository. I explain how to write visual testing using open source tools in this [blog post](https://glebbahmutov.com/blog/open-source-visual-testing-of-components/) and [slides](https://slides.com/bahmutov/i-see-what-is-going-on).
 
 ## Common problems