perks sync docs are out of date

so, normally, perks in donate and civicrm should just sync magically, but this is not working so well (ProductAttribute json/api structure and minimum... (#53 - closed)). instead, before leaving stephen did some work to write up some docs on how to do this by hand (docs: Document how to treat exported perk data ... (tpo/tpa/wiki-replica!67 - merged)) which i merged recently.

originally, i had a few comments on the docs, which i spun off in an issue (Follow-up from "docs: Document how to treat exp... (tpo/tpa/wiki-replica#4 - closed)) but since then @lavamind told me even those docs are not really relevant because they're not really the way it's done anymore.

still, we should have some docs. and because bad docs are better than no docs at all, i made this issue and added a pointer in the docs to here.