Add design principles doc

[franniez]

As suggested in https://github.com/github/the-open-source-survey/issues/6, this doc outlines some basic principles about how we plan to field this survey, including (so far)

• a basic definition of the universe of the study
• the primacy of respondent privacy
• comparability to other work as a goal
• random sampling
• intention to field in multiple languages
• goals for a good and minimally disruptive respondent experience

@arfon @bkeepers @mlinksva anything else we should add here?

[bkeepers]

This is so great!

Only thing I might add is our (GitHub's) desire to be in a position of least privilege. We want to avoid questions and methods that put us in a privileged position with the data, so long as it doesn't conflict with privacy.

[arfon]

❤️ this. After "and we welcome pointers towards prior work that can inform our design." shall we put a link to the contributing guidelines?

[arfon]

Only thing I might add is our (GitHub's) desire to be in a position of least privilege. We want to avoid questions and methods that put us in a privileged position with the data, so long as it doesn't conflict with privacy.

@bkeepers - yeah, I think that's an important thing to call out.