Add docs for using the grid-intensity-go CLI to changed a cronjob from running regularly at say 6pm, an instead make it find a time between 4 and 9pm, and optimise for lowest grid intensity

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This was asked in the climateAction.tech slack, and I realised it's fairly doable with the grid intensity CLI, using something as simple as cron, an some lateral thinking:

Hi, is it possible to schedule the usage of GCP infrastructure when the energy mix in the region is cleanest? I have been having a look but haven't found too much. Context: I have a job I want to run on a regular cadence (e.g. once every 24 hours) but it doesn't need to be exact ie there could be a 6 hour window. The job will be computationally expensive (ML model re-training). A couple of things I have thought about already:
Schedule job when I know the demand on the grid is low ie overnight
Make use of any shared infra that exists so sharing the same underlying hardware at the expense of longer computation times
Any thoughts/advice appreciated!

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Is should be possible to do this with regular old cron, or anything that can run the same code a few times a day

You'd need:

1. a way to check the current / expected co2 intensity
2. a deadline by which the job has to be run
3. a way to tell if the job has been run already
4. a way to decide to go ahead with a job, and or either abort early

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TODO - there are definitely tools that do this already

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