Add a page with KoboToolbox survey design best practices

[rudokemper]

Based on the experience helping a user build a proper KoboToolbox form, I thought I'd document some of the best practices that I shared with them for future reference / replication, per our decided retreat practice of

"whenever we help a partner with something, is there a way to turn this into something reusable—so the next partner doesn’t need the same help from scratch?"

In doing this I thought to split out a Survey Design Best Practices page from the general Kobo one - as there is, and will be a lot more, to share here.