[logback-dev] [qos-ch/logback] 833c40: Update CONTRIBUTING.md

[Tony Trinh]

  Branch: refs/heads/master
  Home:   https://github.com/qos-ch/logback
  Commit: 833c40faf0aa1b272ebbebf5f6b392e2c505f693
      https://github.com/qos-ch/logback/commit/833c40faf0aa1b272ebbebf5f6b392e2c505f693
  Author: Tony Trinh <tony19 at gmail.com>
  Date:   2014-06-03 (Tue, 03 Jun 2014)

  Changed paths:
    M CONTRIBUTING.md

  Log Message:
  -----------
  Update CONTRIBUTING.md

Warn users against adding their release notes to news.html since that
always causes merge conflicts.