Provide instructions when unable to infer entrypoint in ruby/appengine
Provide instructions when unable to infer entrypoint in ruby/appengine

The warning above already partially covers this, but only the error message is shown to the user in the CLI on deployment failure.

PiperOrigin-RevId: 313796207
Change-Id: I8f9d2e1990966283f7583d5b5acabec28230446d

GoogleCloudPlatform/buildpacks,GoogleCloudPlatform/buildpacks,GoogleCloudPlatform/buildpacks,GoogleCloudPlatform/buildpacks