Handbook: make sure changes outside of product groups are QA'd

Recent change that missed QA:
- #14899 (comment)

handbook/company/product-groups.md

@@ -81,6 +81,7 @@ To make a change to Fleet:
 - Then, it will be [drafted](https://fleetdm.com/handbook/company/product-groups#drafting) (planned).
 - Next, it will be [implemented](https://fleetdm.com/handbook/company/product-groups#implementing) and [released](https://fleetdm.com/handbook/engineering#release-process).
 
+> Ocassionally, a contributor outside of the [product groups](https://fleetdm.com/handbook/product-groups#current-product-groups) (open source contributor, member of the Customer success team, etc.) will implement a change that was prioritized and drafted. On the user story for these changes, add the product group label (e.g. `#g-endpoint-ops`, `#g-mdm`), the `:release` label, and notify the product group's Engineer Manager to make sure the changes go through testing (QA) before release.
 
 ### Planned and unplanned changes