Add QCon conference data

[artrmkr]

/claim #11

Summary

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

Source notes

• QCon conference family: https://qconferences.com/
• C4Media identifies QCon as part of its conference/event work: https://c4media.com/
• QCon London speaker support says QCon offers budget for speaker travel and accommodation arrangements: https://qconlondon.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 note: this is a static README data update, so the PR diff is the review/demo surface.

[artrmkr]

Hi @jdegoes, just following up on PR #335 for #11.

It adds QCon with current QCon/C4Media public sources, preserves the README table schema, includes /claim #11, and includes validation notes for the table column-count check, git diff --check, and HTTP 200 source-link checks.

Happy to adjust anything you want changed before review/reward. Thanks!