If someone is interested in writing up a quick introduction to ASDF configuration of input and output, I will be willing to help get it into the texinfo manual, if texinfo wrangling is what's needed.
Unfortunately, I cannot do this myself, because I don't use the input configuration --- my company developed a standard protocol for manipulating ASDF:*CENTRAL-REGISTRY*, and that ain't broke, so we aren't experimenting with the input locations...
:-/
Best, R