Clarify what students should put in 'Affiliation'

I get questions from students and other volunteer contributors to OpenStack or simply Individual Member that are not paid to work on OpenStack about what they should put on 'Affiliation' when they sign up. The explanation text says:

"For our purposes, an affiliation is defined as any company where you are an officer, director or employee, or any person or company that has paid you more than $60,000 USD as an independent contractor in the last 12 months. Please list all affiliations which meet this criteria."

I think it may be helpful to add that if you're not being paid to work on OpenStack please put "Unaffiliated".