Add information about incubation mailing list to handbook
@wbeaton
Submitted by Wayne Beaton Link to original bug (#483809)
Description
Let's point new committers to the incubation@eclipse.org mailing list.
https://dev.eclipse.org/mailman/listinfo/incubation
I think that this fits well into the "Starting an Open Source Project" section.
Where else? I think that we need a "so you're a new committer" section.