https://gbatemp.net/threads/nintendo-switch-sd-to-nsp-dumper.514816/ for a more automated and easier way to do this
This guide assumes you have previous experience with hactool and messing with your NAND. You aren't supposed to blindly copy commands in this, so read before pasting!
Also, the Python sections require Python 2.7 and pycrypto. Make sure your hactool is v1.2 or above.