Feature - Provide the ability for users to "ask" for some columns/models to be documented

[b-per]

A bit more far fetched, but tangata could potentially be used for people to request for models/columns to be documented.

A simplistic solution could be to store a specific string (like TODO) in the schema.yml for the model/column and having the ability to search for those TODO items in tangata.

[ciejer]

Relies on #29 - will use meta tags to keep things usable elsewhere in the dbt context.

In the meantime, added a promoted models pane on landing page - this will be a good format to display these also.