Add QCon conference data

[snkk2x-collab]

/claim #11

Summary

• Add QCon to the conference dataset.
• Preserve the existing six-column README table schema.
• Use conservative SEA and speaker-fee values because I did not find public commitments for those policies.

Source notes

• QCon conference family: https://qconferences.com/
• C4Media identifies QCon as part of its conference/event work: https://c4media.com/
• QCon speaker support says QCon offers budget for speaker travel and accommodation arrangements: https://qconsf.com/qcon-cares

Verification

• python3 README table check: 12 conference rows, all with 6 columns.
• git diff --check
• Source link check: 3 QCon/C4Media source URLs returned HTTP 200.

Demo

Static README data update; the PR diff is the review/demo surface.

AI-assisted implementation, manually source-checked and reviewed before submission.