Add QCon conference data

[CharlieLZ]

/claim #11

Summary

• Add QCon to the conference dataset.
• Preserve the existing README table schema.
• Use conservative SEA and speaker-fee values where no public commitment was found.

Source notes

• QCon conference family: https://qconferences.com/
• C4Media homepage identifies QCon attendee/speaker resources and the company: https://c4media.com/
• QCon London speaker support says QCon budgets for speaker travel and accommodation arrangements: https://qconlondon.com/qcon-cares
• Historical QCon speaker information shows speaker registration/fee coverage and hotel coverage: https://qconsf.com/sf2010/sf2010/speakerinformation/index.html

Verification

• rg -n "QCon" README.md
• awk README table pipe-count check: all table rows have 6 columns.
• git diff --check
• Source link check with curl -fsSL --connect-timeout 10 --max-time 30 -o /dev/null for all cited source URLs.

Demo

• Static data update demo/validation video: https://github.com/CharlieLZ/conference-data/releases/download/conference-data-350-351-demo/conference-data-350-351-demo.mp4

Demo note: this is a static README data update, so the PR diff is the review surface.