Add link to "health and happiness in the lab" article

[jeremymanning]

Here: https://www.nature.com/articles/d41586-018-07514-7?code=bea691cd-8bc3-4ed6-8ec6-007755bead90&error=cookies_not_supported

[jeremymanning]

Also potentially incorporate some of these ideas

[paxtonfitzpatrick]

@jeremymanning do you still want to add this? The lab manual currently does include one required reading on "lab culture" (Leah Somerville's article) and I want to be cautious about making the on-boarding process too time-intensive.