Dvc.org: document `dvc import` and `dvc get` (previously `pkg` commands)

[efiop]

UPDATE: See description in https://github.com/iterative/dvc/pull/2160 instead.

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OLD: Some introductory descriptions for DVC packages (from Discord):

You have project named awesome_project, which has awesome_data in it
pkg will allow you to "import" the project
dvc pkg import awesome_project://awesome_data (syntax may be incorrect)

1. Any DVC repo is a _package_. Outputs inside packages can be called _artifacts_ (that we'll also be able to work with)
2. There will be a set of commands to import/export these _packages_ across different repositories and from a repository to a file system (just a data artifact)
3. basic use cases include things like: dataset registry (reuse a single dataset in multiple project, while having a single point of responsibility for the dataset itself), easy mechanism to pull a data artifact w/o doing git clone + dvc pull data.dvc, etc
4. in the future (no need to focus on this for now) any set of DVC files will be considered as package, thus making pipelines reusable

[jorgeorpinel]

Main references found in core repo:

• https://github.com/iterative/dvc/pull/1742 "Pkg install" PR (merged)
• + https://github.com/iterative/dvc/issues/1772 "test: pkg: add func test" issue (open as of now)
• https://github.com/iterative/dvc/pull/2012 "Initial pkg implementation" PR (open as of now)

Also, funny: dvc pkg doesn't have a -h option. Is that normal? Opened https://github.com/iterative/dvc/issues/2065

[efiop]

@jorgeorpinel Sorry for the confusion, the PR that this relates to is https://github.com/iterative/dvc/pull/2012 , which is not merged yet. I've just created this task in advance.

[jorgeorpinel]

Oh. @shcheklein asked me to give this one priority. Are you saying I should wait for that PR to close first Ruslan? Makes sense to me 😃 although I already opened a WIP PR for this 😋 (#388)

[shcheklein]

@jorgeorpinel this is a priority :) we will see if we merge it before pkg code is merged or not. It will also take some time to get the docs for it done end-to-end. It's a big feature.

[efiop]

• [x] Note: also need to make sure to add a note that old import was moved to import-url.