Consider more thorough review guidelines

[sgibson91]

Currently, we say mentors will follow Outreachy's recommendations

• https://jupyterhub-outreachy.readthedocs.io/en/latest/mentors/application-review.html#guidelines-for-reviewing-applications
• https://www.outreachy.org/docs/applicant/#contribution-evaluation

Is there anything that is not covered there that we think should be? Should we be more specific?

Here are some example guidelines from other communities: http://intermine.org/internships/guidance/grading-criteria-2021/
(Note: I think Project & Plan refers to GSoC where the applicants write their own project proposals, not so relevant for Outreachy)