Splash page

Thanks for the quick feedback on my last pull request!

This is some modifications to [#829](https://github.com/vhf/free-programming-books/pull/829).  Pulling the course that I added into a separate file called `free-courses-en.md`.  Once I built this file, I moved a handful of free video courses that belong here from `free-programming-books.md`.

I didn't rebase these different changes, because the contribution guide suggests leaving the individual changes.

Let me know if there are any changes to make, happy to make them :smile: