Provide guidance for the `metaRobots` field

[illright]

Right now, when you add the SEO component, you are presented with a bunch of fields with no descriptions. For most fields, it's not a big deal, but the metaRobots fields leaves me completely baffled as to what values it might expect. I've seen in another issue thread that you can use this field to prevent indexing by writing noindex, but I find myself scratching my head as to the exact syntax of how to write it, commas, spaces, quotes, etc.

Could you please provide a description that explains the syntax of this field (maybe with a link to a more detailed explanation) and a useful placeholder to get a feel for the syntax quickly?