Change Start workflow screenshot for sth that is functional

[ChucklesOnGitHub]

I know it's intended to be general Bonsai usage, but the screenshot here makes it look like actually attempting this would be successful:
https://open-ephys.github.io/bonsai-onix1-docs/articles/getting-started/start-workflow.html

I'd use the workflow from the last comment from the previous section and overlay the Start button box over that.

We got this as a support request, and I can see it happening for ppl who are eager to test their system and are reading the User Guide before reading the Hardware Guide.