Add a note regarding groups with multiple owners to namesquatting workflow

Why is this change being made?

For situation where there are several owners to a group, we need to contact each owners individually. See slack thread :

Ségolène Delaby Bouly: [Name squatting question] For group with several owners, should we contact all of them in one ticket or only one owner or multiple tickets?

Ségolène Delaby Bouly: I am going for multiple tickets so I not share emails addresses

Cynthia 'Arty' Ng: you know, I think we used to have 1 ticket for multiple owners, but that's a good point. Could you update the handbook? Feel free to set me as reviewer.
Also, I usually limit it to the earliest 3-5 owners because some groups had a lot.  

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