Save-the-dates for HEW/HIW 2027

[LaurentRDC]

Fixes #637

[dschrempf]

Thank you Laurent, and sorry for not being faster, I am a bit tight on time these days.

Minor suggestions:

• "Talks have been scheduled to account for this.": Maybe drop the sentence or change it to "will be".

• "we'll let you know which additional spaces are good for compiler hacking": Should be deleted, I think.

[LaurentRDC]

Thanks Dominik. No worries about being constrained on time!

I will also add an annoucement in this same PR