Add a guide which highlights how to handle action's outputs by writing
them to the client filesystem and using CUE's integrations to marshal
them as JSON.
Signed-off-by: Marcos Lilljedahl <marcosnils@gmail.com>
The reference to `docker.Copy` does not exist and should be `docker.#Copy` instead. This also leads to a confusing error message (possibly related to #493) as it isn't found while CUE is compiled, and instead results in the following runtime error:
```
[✗] actions.deps 2.1s
9:16PM FTL failed to execute plan: task failed: actions.deps._dag."2"._exec: invalid FS at path "actions.deps._dag.\"2\"._exec.input": FS is not set
```
Signed-off-by: Ben Gesoff <ben@gesoff.uk>
