Update docs for new frictionless workflow

[noamross]

README and vignettes will need to be updated to reflect the frictionless approach. Better to to this sooner than later so we can get some more folks informally testing/contributing.

[mpadge]

Prior to that:

TODO:

• [x] Allow a frictionless-less workflow, by by-passing all frictionless stuff whenever frictionless::add_resource() errors (on anything that can't be parsed as a rectangular text file).

That will allow the broader, initial docs to remain general, before moving quickly on to a "frictionless workflows" section declaring that deposits is primarily intended to be work with frictionless.

[mpadge]

This should be the last point here:

TODO

• [x] Write new vignette on the frictionless workflow, including demonstrations of how to locally edit the "datapackage.json" file, and update remote version.

[mpadge]

Nope, one more point to go along with that:

TODO

• [x] Add new deposit_update_frictionless() function to allow client metadata to be directly edited, and changes propagated through to local and remote versions of "datapackage.json"

[mpadge]

Should now be very final:

TODO:

• [x] Add tests for new deposit_update_frictionless() method

[mpadge]

Done