Learning to program for a 6502 computer
The following are some helpful online resources for learning 6502 programming:
A brief guide to programming the 6502 in assembly language: http://www.dwheeler.com/6502/oneelkruns/asm1step.html
6502 opcode summary: http://www.6502.org/tutorials/6502opcodes.html
Code samples: http://6502.org/source/
Complete step-by-step tutorial: http://skilldrick.github.io/easy6502/
Emulated programs: http://www.6502asm.com/
Note: the above tutorials and emulators are not designed with the same memory mapping as the Wasteland 2 computer. You won't be able to use those programs directly, but they are a great resource for learning.
Next, you'll need to get some tools together to assemble your programs into opcode and compile them into a binary file called "Diskette". Check out this thread.