[Cython] Pull request emails

[Dag Sverre Seljebotn]

Finally think I figured out how to get pull request emails (thanks to 
Gael V). From https://github.com/organizations/cython/teams/24445:

"""
Owners do not receive notifications for the organization's repos by 
default. To receive notifications, create a team and add the owners and 
repos for which notifications are desired.
"""

I created Reviewers and added me, Stefan & Robert for now.

https://github.com/organizations/cython/teams/54516

Dag Sverre