Update Regular Files API to reflect new add / addAll distinctions

[terichadbourne]

BLOCKED

We've done what we can to update the text of the Regular Files API tutorial to reflect the intended usage of the add and addAll, but in actually they both appear to be accepting both single file objects and arrays of file objects. The js-ipfs team is still finalizing how these methods will work and what will throw errors, so we'll need to update our validation once that's been settled.

See related js-ipfs issues:
ipfs/js-ipfs#3195
ipfs/js-ipfs#3188

@achingbrain can you please update us when things settle out on your end so we can make the appropriate updates in our validation?

[terichadbourne]

@achingbrain Just checking in to see if there's been any movement on what add and addAll will actually accept.