Add app dev how-to for specifying export target along with diagram

showing how pack uses the daemon.

Signed-off-by: Natalie Arellano <[email protected]>

Author: Natalie Arellano

content/docs/for-app-developers/how-to/build-inputs/specify-export-target.md

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+title="Specify export target"
+weight=50
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+
+Tell `pack` where you want your application image to be saved.
+
+<!--more-->
+
+By default, when you `pack build` an application, the image will be saved to a daemon, such as Docker or [Podman][podman],
+and you can view the image using a command such as `docker image ls`.
+
+However, you could also choose to "publish" the application to an OCI registry, such as Docker Hub or Google Artifact Registry,
+or even to a local registry, by providing the `pack build --publish` flag.
+
+Or, you could save the image in OCI layout format on disk by providing the `--layout` flag.
+See [here][OCI layout] for more information about working with layout images.
+
+## FAQ: What am I using the daemon for?
+
+Buildpacks always need to run in a containerized environment.
+Therefore, even when you publish the application image to a registry,
+`pack` is still using a daemon under the hood to create the build container(s) where buildpacks run.
+
+The relationship between the build container and the application container can be seen in the diagram below:
+
+![build diagram](/images/build-container-app-container.svg)
+
+[podman]: /docs/for-app-developers/how-to/special-cases/build-on-podman
+[OCI layout]: /docs/for-app-developers/how-to/special-cases/export-to-oci-layout