README: add goals and how we think about design

[lognaturel]

Some starting points: #2 (comment)

[lognaturel]

Notes on how I've been thinking about introducing new library methods:

• Is it common enough to warrant a designed method or can we show examples using the HTTP methods if needed?
  • E.g. manipulating form drafts directly is out of scope (but client.forms.update implicitly creates and publishes a draft)
• Do people take this action independently or is it always part of reaching some broader goal?
  • E.g. draft publish doesn’t need to be exposed on its own but it is part of updating a form
• What class does it best fit in?
  • E.g. form versions are subresources on Central backend but in this library, methods that deal with form versions can be in the forms class directly since we’re not going to expose many of them
• How do people talk about the action that’s being performed? How do ODK docs and Central frontend talk about it?
  • E.g. we have the concept of “submission edits” so use client.submissions.edit rather than update
• Value expressiveness and consistency with ODK concepts over internal consistency
  • What actually needs to be commonly configured? Starting by exposing a subset of parameters and naming/typing them carefully is ideal.