Add documentation to polars datasets explaining how to use OmegaConf resolvers

[datajoely]

Description

Is your feature request related to a problem? A clear and concise description of what the problem is: "I'm always frustrated when ..."

See user issue here: #884 (comment)

We actually document custom polars resolvers in the resolvers documentation, but it's very easy for a user to never see this. The user suggested to put this in the dataset(s) docstring which I think is a great idea.

Possible Alternatives

(Optional) Describe any alternative solutions or features you've considered.

Link to resolvers in the YAML rather than recreating it