Encourage collaboration when working on promo docs

Why is this change being made?

While working on my own promotion (document), I noticed that I felt oddly secretive about the whole process. I started a discussion about this within my team, suggesting that we be more explicit about the fact that collaborating is allowed and encouraged here as well. The feedback was very positive, so this MR is my suggestion on how this could be worded.

Author Checklist

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