Add Brian Williams as a Merge Request Coach

MR coach application

1. Why you want to become a Merge Request Coach?
   1. I'm interested in helping out contributors
   2. I already monitor the #mr-coaches and #gitter-contributors-room channels and frequently review community contributions
   3. If a join the team, then ~"group::container security" will have both a frontend and backend coach
2. How much time you are planning to spend on it?
   1. A couple of hours per week
3. Which duties you are focusing on (e.g. triage, finish stale MRs)?
   1. Triaging community MRs and assigning reviewers
   2. Performing code reviews
   3. Monitoring #gitter-contributors-room and answering contributor questions

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