Contributor guidelines: need to write document explaining how to introduce wire format changes

[Aaronontheweb]

An example of where I goofed and approved a wire format change that should have been handled differently:

Hi @Martin-Molinero - this looks like a new version --> old version breaking wire format change that we caused, and the reason why is because we standardized the the primitive type manifests because they varied between .NET Core and .NET Framework due to the breaking changes Microsoft introduced at the inception of .NET Core.

We're really sorry about this - we probably should have made this an opt-in feature some months after introducing this serializer so you wouldn't be hit with this issue during a live upgrade. The work around for this now is probably to either just bite the bullet and upgrade everything, or to override this serializer with the one from the v1.4.19 source code and drop it later.

Originally posted by @Aaronontheweb in #4989 (comment)

Need to write some contributor guidelines that explain how to do this safely so users don't run into wire format compatibility issues between upgrades.