I personally didn't know the very exact expression, but I can make a reasonable guess that it's a variant of サルでも…… ("Even monkeys do..."). The implication is quite similar to "for dummies" in English, which is to state its easiness in exaggerated manner.
One of web pages using the phrase declares:
There were some (books?) like "~~ For Monkeys" quite some time ago, but we'll go much farther. Bookkeeping For Crabs! You don't even need to be a mammal!
By the way I'd like to add that my favorite one is ヤドンでもできるポケモン乱数調整 ("Pokémon RNG Manipulation for Slowpokes").