Add QCon to conference data tracker

[junbuilds96]

Summary

/claim #11

Adds QCon to the conference data tracker using public QCon/C4Media sources.

Source notes

• Conference page: https://qconferences.com/
• Organizer: https://c4media.com/
• Public QCon speaker-support materials indicate QCon/C4Media handles conference access and travel/accommodation support for speakers.
• I did not find public evidence that QCon signs the Speaker Engagement Agreement, so this uses No conservatively per the issue guidance.
• I did not find a general public speaker-fee policy, so compensation is Never.

Validation

• Preserved the existing Markdown table schema.
• Inserted QCon before ScalarConf in the current table order.
• Ran git diff --check -- README.md.