Update content.md

[andanders]

correct filename

[tianon]

In the future, please update your existing pull request instead of creating a new one (#2534; https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/creating-a-pull-request#making-changes-to-files-in-your-pull-request).

cc ros image maintainer @tfoote -- this looks correct to me, but I'd love if you could confirm 🙇

[tfoote]

This is rolling back to the old syntax. We switched to the _launch format 2 years ago: ros2/demos#588 This should be the correct syntax for all versions after Humble.

We could add a side comment for Humble and older to use the alternative syntax, and support that until Humble goes EOL. But I would be inclined to keep this as targeted for the default version.

What's your usage @andanders ?