Fix redirects

[jarrodmillman]

https://scipy-lectures.org/ redirects to https://lectures.scientific-python.org/, but
https://scipy-lectures.org/intro/ doesn't redirect.

[stefanv]

This is because we haven't rebuilt the site with the redirect feature yet. I just manually added a root page redirect: scipy-lectures/scipy-lectures.github.com@3485dea

[stefanv]

Thinking about it, is a redirect at every level a good idea? Perhaps a banner instead, so that links to old material remain functional?

[jarrodmillman]

I am not sure it makes sense to keep the old material around. It is already pretty out-of-date and will only get worse.

[stefanv]

The easiest option is to rebuild then to get all the redirects in place. The risk is that those redirects may grow stale with time.

Another option is to write in the redirects by hand, as we did for the main page.