Why is this a bad idea?

Those books were already scanned and it adds nothing. A useful skill describes some specific tool or RAG info your app needs. There's no value add in just making an overly long prompt which is what your skill will do.

In realty, skills, MCP, and other techniques for harnessing agents are themselves just prompts. In this case, adding "read this book" the prompt is unhelpful, it pollutes context, and it distracts the LLM from the unique carve outs and special situations your code does have because you're prompting about boilerplate, standard stuff.