Review

It's great work! Congratulations!

My comments will be related mostly to organizational things and some minor codebase details.

Codebase

A few notes regarding the functionality:

it allows saving a zip archive, a descriptor, and a readme. I would consider also adding a method to save the data itself.
it seems there is a typo in the readme if da.valid(): -> if da.valid:

Here are my recommendations regarding the repository:

renaming the repo and the lib to something like datapackage-dwca/darwin/etc to be aligned with our naming conventions
following the oki-py repo structure regarding files like Makefile etc. Maybe the more up-to-date example is datapacakge-py. Using this approach ensures that all community members are able to work with the repo using familiar commands like make test , established releasing technics, etc
setting up TravisCI and Coveralls for continuous testing and releasing (I've enabled them for the repo). So the missing parts are travis.yml, readme's badges, etc
releasing the repo to PyPi following the SemVer versioning approach

PS. It's a long shot but I'm curious whether it can support the Storage API also (maybe in the future):

cc @lwinfree @andrejjh