I think the reason there is no System requirements listed is because GD can run on almost anything really there is only very few requirements that most if not all PC from the last 5 years can meet easily.
CPU: any 64bit compatible CPU
RAM: 1GB RAM (for GD itslef, the game you are making depends on you)
GPU: any WebGL compatible graphics
OS: any 64bit operating system, more recent the better
If you can find a laptop with a WebGL compatible graphics running a 64bit operating system, it should be fine imo.
If you share a link to the computers you looking to buy we can help you choose.