Revise NixCon 2026 sponsorship details (only organisers version)

[infinisil]

Note

Alternative to #251
This version does not allow volunteers with responsibilities to discuss sponsors before they're approved/rejected

It's not ideal how the 2026 sponsorship tiers were changed without updating the document here. I'm also not sure how the changes were decided, but I don't think they need SC/board approval, so fine by me :)

The more important change here is a simplified sponsorship approval process with much lower bureaucracy compared to last years.

@NixOS/steering Please majority approve
@ners @john-rodewald @Lassulus @Ra33it0 Please approve

[philiptaron]

No feedback, this is good.

[infinisil]

Fyi, I just noticed that since this year only @ners @john-rodewald @Ra33it0 @Lassulus are listed as organisers on the website, which means other volunteers with responsibilities wouldn't have a chance to be involved in reviewing sponsorships like last year.

I didn't know about this difference beforehand, so in case the other version is preferred by the approvers, I now created #251 as an alternative. From a board perspective, I don't really care how it's done in the end, I'm just making the PR so we're all clear about the process. So in case you run into sponsorship conflicts later because of this, please keep me out of this 😆

[ners]

Thank you for the diligence @infinisil!