Update source/handbook/people-group/promotions-transfers/index.html.md

Why is this change being made?

To make sure Hellosign setting has been checked before the staging the letter. This setting initiates the process in sequence and order.

Replaced company call with Slack #team-member-updates channel.

cc: @gl-compensation @cteskey

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