add information for international students

[jeremymanning]

According to OVIS, international students in the US on certain VISA categories cannot do volunteer work. This may impact these students' abilities to volunteer in the lab. We should add a (sub) section to the lab manual describing:

• What the current policy is (to the best of our current understanding), with a link to any relevant OVIS documentation
• Workarounds that have been successful in the past:
  • Course credit: independent studies and/or thesis projects
  • Leave term and/or on-term grants through UGAR, Neukom, etc.
• Categories of student that we don't have good workarounds for yet:
  • First year international students who do not want to (or can't) sign up for independent studies; all of the Dartmouth grants seem to require second-year status or beyond

[jeremymanning]

We should also include information on visiting scholars, like @xinmingxu's position last year...