Document OPAQUE in clash-prelude API documentation #3104
Description
When you want the Clash compiler to make a separate file for a function you can annotate the function with an OPAQUE pragma. Currently, this only seems to be documented in either the user guide or the tutorial. It probably should be documented in the clash-prelude API as well. Places we could consider:
Clash.Annotations.SynthesisAttributesClash.Annotations.TopEntityClash.Annotations.Primitive
We could simply link back to the relevant section of the user-guide/tutorial from those places.