Credit GSoC mentors in the "mentoring" team (#425)

I propose we include a link to the GSoC wiki page stating who is mentoring for the year in order to acknowledge folks volunteering to mentor/admin. I have included a link to the wiki so that this will be updated when we update things for the GSoC program, but we can also write individual names here if that is preferred (though it will be harder to keep up-to-date imo)

_data/team/roles/outreach.yml

@@ -20,6 +20,7 @@ subroles:
       - "[Brady Johnston](https://github.com/bradyajohnston)"
       - "[Egor Marin](https://github.com/marinegor)"
       - "[Jenna Swarthout Goddard](https://github.com/jennaswa)"
+      - "[Google Summer of Code (GSoC) mentors](https://github.com/MDAnalysis/mdanalysis/wiki/Google-Summer-Of-Code#available-mentors)"
 
   - subrole: Teaching materials
     tasks: