Add to doc: Select Individual Approvers for Merge Request Approvals

Select Individual Approvers for Merge Request Approvals -

https://docs.gitlab.com/ee/user/project/merge_requests/merge_request_approvals.html#merge-request-approvals

From release post copy: Configuring merge request approvals allows for selecting individual approvers. The process is even easier, with the search now limited to project members (this is the new change) and users in relevant groups (parent group or groups with access via a project share) in the project settings and the per merge request settings, so that you can easily identify relevant users. duct.