'forth' is an old word that means 'out'. He set forth on his trip = he set out on his trip The water poured forth = the water poured out 'pouring forth' is often used to capture the idea or imagery of water gushing/leaving/going out of a tap. It is constant, fast, never seeming to end. So must-read literature 'pouring forth' is literature coming out/being released at a fast rate with no pause - like how water 'pours forth'/gushes out of a tap.

Pouring forth here means that many, many more books are coming his way to be read. Pouring here means an overwhelming quantity.