make project06 hack assembler easier to use

[bgx]

• Don't prompt user for the name of .asm file; expect filename as argument when run from commandline
• Print meaningful message when no .asm filename is supplied or filename is incorrect
• .hack files should appear in same directory as .asm files
• create README file with instructionsn for running assembler
• create RUN file with same commands used to run assembler from commandline (ex: python.exe )

[bgx]

https://stackoverflow.com/questions/82831/check-if-a-file-exists-using-python