Link project factory documentation from FAST stage

[ludoo]

Fixes #1628

[gustavovalverde]

I don't think this solves the problem if someone uses the available sample file in the stage:

• https://github.com/GoogleCloudPlatform/cloud-foundation-fabric/blob/master/fast/stages/3-project-factory/dev/data/projects/project.yaml.sample

Most people would commonly adapt the sample to their use case, but if the sample has the wrong data types, then it will crash for newcomers, unless they start digging into each dependency and their documentation.

I'm using that same file structure, as shared here:

• stages: document how the new factory_data is meant to be used #1628 (comment)

I would say adapting the file would be the missing part, as done here:

• 12e78af#diff-8ad613bbda56823204e080e67cdab397ff19531aecb7c1a3faa06c74858f2899

[ludoo]

Good point, let me nuke the stale file out of existence. :)