Add header following Go convention for generated code (#21)
Add header following Go convention for generated code (#21)

Go has a convention for generated code comments
(https://golang.org/s/generatedcode), i.e. they must match the regex
^// Code generated .* DO NOT EDIT\.$

Adjust the generated header to follow this convention.
riscv/riscv-opcodes,riscv/riscv-opcodes