Document usage of `yaqb_codegen`
Document usage of `yaqb_codegen`

I've left off associations for now, as I'm actually wondering if it
makes more sense to annotate the table rather than the model. I'm going
to see if this is possible.

sgrif/diesel,cascalheira/diesel,cascalheira/diesel,mcasper/diesel,diesel-rs/diesel,sgrif/diesel,tohou/diesel,SoftwareWarlock/diesel,tohou/diesel,mcasper/diesel,diesel-rs/diesel,SoftwareWarlock/diesel