Add language in the editor guide about finding reviewers - 1 domain 1 can be usability etc

[lwasser]

Right now i normally tell people that the 2 reviewers can be split

1. can be domain specific / python
2. second can be more usability / packaging. / python

And we want to ensure diversity. i think we need to update the editor guide to cover this topic. And also the finding reviewrs language is either missing or hard to find.