FIRRTL Rationale

[dtzSiFive]

We should add a place to document the "Rationale" for FIRRTL's design, perhaps in the spirit of MLIR's rationales: https://mlir.llvm.org/docs/Rationale/ .

This has been proposed and requested by a number of folks actively contributing to the specification, and let's start sorting out what this might look like and where.

[dtzSiFive]

One candidate detail to include in such a rationale would be the motivation around some of the reference type design (under assumption it's merged of course), probably in general but specifically regarding input probe types. Request: #75 (comment)

[seldridge]

#147 improves how block quotations are rendered to make them look like RISC-V Specification commentary blocks (an italicized region with increased left and right indentation and a rule at the top). This may help fill the gap for things which are explanatory, but outside the realm of what should be discussed in the spec.