Add Maintenance Documentation for Forgetful Maintainers

[zandi]

Just to save time with research & finding references for the next time I add or fix something.

Useful Linux kernel bpf files (primary bpf 'user' is linux kernel, absolutely must support it):
https://elixir.bootlin.com/linux/latest/source/kernel/bpf/disasm.c
https://elixir.bootlin.com/linux/latest/source/include/uapi/linux/bpf.h
https://elixir.bootlin.com/linux/latest/source/include/uapi/linux/bpf_common.h

LLVM BPF instruction definitions. There's other nifty looking files nearby as well:
https://github.com/llvm/llvm-project/blob/main/llvm/lib/Target/BPF/BPFInstrInfo.td