Link to Package Generator #49

In the Choose a Device Module section, we reference creating a package via code generation multiple times and explain the benefit vs device module generation at runtime, but we don't actually link or reference how to do this step. While it's out-of-scope for this metapackage, it's worth at least linking to the code generator or linking to a set of instructions for applying the code generation approach with a device.yml.

A generated device package is a real Python module on disk, produced from a device.yml by the Harp code generators [...]

It would be perfect to link out to a way to do code generation somewhere in the section quoted above.