A couple of corrections for you Sylvain,
Copyleft - using copyright terms to REQUIRE that copies retain the same license no matter how it's modified or re-copied. GPL and Creative Commons Share-alike are copyleft. Apache, MIT and Creative Commons Attribution are not copyleft licences. Although all are open source and Free Software licenses.
About us, we didn't plan to copy your content at all, at least for the moment, but libre content is always appreciated.
We require permission to make copies for all content on the website. Because delivering content makes a copy upon each request. When you view a website's contents you are making a copy.
A link is ok though, and like you say it's easy enough to link. But it's more helpful I think to consider digesting good content into our docs rather than linking. Because we're more likely to maintain things centrally and be able to apply upgrades in visual appearance and translations.
I just added a link to your tutorial on the Inkscape wiki (there's probably not much restriction for it) — that wiki whose hundreds of dead links from years and incorrectly formatted contents really scare me —: http://wiki.inkscape.org/wiki/index.php/Tutorials_and_help#English_.2 8en.29
The wiki is dedicated to inkscape development. So tutorials about inkscape development (coding, website devel, writing docs) makes sense. But tutorials about how inkscape can be used should go on the website itself.
You can use the wiki to plan out or draft content though, as long as the intention is that it'll end up on our public facing website at some point.
Best Regards, Martin Owens