Add effects description to instructions up close chapter

[tomaz]

At the moment it's not immediately clear for beginner what standard effects are, user has to go to the chapter start page to remember. So maybe add short description at each relevant instruction? Or maybe description of various use cases like what JP NZ, JP Z and others would have AFTER the instruction?

[tomaz]

Each instruction now includes description of flag effects, some have further details and code samples. Still work to do, but it's a good update compared to previous version; maybe in future revisions.