Add Mitch M. to team page

Why is this change being made?

Mitchel Nielson will be joining GitLab on April 6, 2020 https://gitlab.com/gitlab-com/team-member-epics/employment/-/issues/1939

This change adds a stubbed entry for Mitch to be updated per onboarding instructions.

Does this MR meet the acceptance criteria?

Assign to DRI

• Did you assign this change to the correct DRI of the page or information you are changing?

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what