Docs: Add a tutorial dedicated to the "default plugin + multiple binaries" scenario

[sed-i]

What needs to get done

Go and rust projects often pack perfectly fine by using the plugins.
Often, there are multiple binaries produced by go build or cargo build.
Please add a tutorial that walks users through:

1. Setting up a minimal snapcraft.yaml that uses just the plugin.
2. Poking through the parts as they are built in search of the binaries. I.e. how am I supposed to know to use command: bin/my_app? And what about other binaries? I'd like to see what are their names and prime (?) them as well.

Just as an example, moving from using the plugin as is, to packing several binaries is not trivial.
Almost every line in that diff went through a failed pack.

Why it needs to get done

Craft-parts can be challenging to grasp, so it would help a lot to have a basic tutorial that guides the user through a discovery process.